Some improvements to copying of newer configuration to current folder:

1) Less context is kept in GUI_App.
2) Copying is not being done if loading current PrusaSlicer.ini fails
3) AppConfig (PrusaSlicer.ini) is saved first after the newer configuration is installed.

src/slic3r/GUI/GUI_App.cpp

@@ -909,17 +909,18 @@ void GUI_App::init_app_config()
                     "\n\n" + app_config->config_path() + "\n\n" + error);
             }
         }
-        // Save orig_version here, so its empty if no app_config existed before this run.
-        m_last_config_version = app_config->orig_version();//parse_semver_from_ini(app_config->config_path());
     }
 }
 
-// returns true if found newer version and user agreed to use it
+// returns old config path to copy from if such exists,
-bool GUI_App::check_older_app_config(Semver current_version, bool backup)
+// returns an empty string if such config path does not exists or if it cannot be loaded.
+std::string GUI_App::check_older_app_config(Semver current_version, bool backup)
 {
+    std::string older_data_dir_path;
+
     // If the config folder is redefined - do not check
     if (m_datadir_redefined)
-        return false;
+        return {};
 
     // find other version app config (alpha / beta / release)
     std::string             config_path = app_config->config_path();
@@ -940,13 +941,13 @@ bool GUI_App::check_older_app_config(Semver current_version, bool backup)
             boost::optional<Semver>other_semver = parse_semver_from_ini(candidate.string());
             if (other_semver && *other_semver > last_semver) {
                 last_semver = *other_semver;
-                m_older_data_dir_path = candidate.parent_path().string();
+                older_data_dir_path = candidate.parent_path().string();
             }
         }
     }
-    if (m_older_data_dir_path.empty())
+    if (older_data_dir_path.empty())
-        return false;
+        return {};
-    BOOST_LOG_TRIVIAL(info) << "last app config file used: " << m_older_data_dir_path;
+    BOOST_LOG_TRIVIAL(info) << "last app config file used: " << older_data_dir_path;
     // ask about using older data folder
 
     InfoDialog msg(nullptr
@@ -959,13 +960,13 @@ bool GUI_App::check_older_app_config(Semver current_version, bool backup)
             "\n\nShall the newer configuration be imported?"
             "\nIf so, your active configuration will be backed up before importing the new configuration."
         )
-            , SLIC3R_APP_NAME, current_version.to_string(), m_older_data_dir_path, last_semver.to_string())
+            , SLIC3R_APP_NAME, current_version.to_string(), older_data_dir_path, last_semver.to_string())
         : format_wxstr(_L(
             "An existing configuration was found in <b>%3%</b>"
             "\ncreated by <b>%1% %2%</b>."
             "\n\nShall this configuration be imported?"
         )
-            , SLIC3R_APP_NAME, last_semver.to_string(), m_older_data_dir_path)
+            , SLIC3R_APP_NAME, last_semver.to_string(), older_data_dir_path)
         , true, wxYES_NO);
 
     if (backup) {
@@ -989,10 +990,10 @@ bool GUI_App::check_older_app_config(Semver current_version, bool backup)
                 BOOST_LOG_TRIVIAL(error) << "Failed to take congiguration snapshot: ";
         }
 
-        // This will tell later (when config folder structure is sure to exists) to copy files from m_older_data_dir_path
+        // This will tell later (when config folder structure is sure to exists) to copy files from older_data_dir_path
         m_init_app_config_from_older = true;
         // load app config from older file
-        std::string error = app_config->load((boost::filesystem::path(m_older_data_dir_path) / filename).string());
+        std::string error = app_config->load((boost::filesystem::path(older_data_dir_path) / filename).string());
         if (!error.empty()) {
             // Error while parsing config file. We'll customize the error message and rethrow to be displayed.
             if (is_editor()) {
@@ -1011,14 +1012,9 @@ bool GUI_App::check_older_app_config(Semver current_version, bool backup)
         if (!snapshot_id.empty())
             app_config->set("on_snapshot", snapshot_id);
         m_app_conf_exists = true;
-        return true;
+        return older_data_dir_path;
     }
-    return false;
+    return {};
-}
-
-void GUI_App::copy_older_config()
-{
-    preset_bundle->copy_files(m_older_data_dir_path);
 }
 
 void GUI_App::init_single_instance_checker(const std::string &name, const std::string &path)
@@ -1117,16 +1113,16 @@ bool GUI_App::on_init_inner()
     init_label_colours();
     init_fonts();
 
-    if (m_last_config_version) {
+    std::string older_data_dir_path;
-        if (*m_last_config_version < *Semver::parse(SLIC3R_VERSION))
+    if (m_app_conf_exists) {
-            check_older_app_config(*m_last_config_version, true);
+        if (app_config->orig_version() && *app_config->orig_version() < *Semver::parse(SLIC3R_VERSION))
+            // Only copying configuration if it was saved with a newer slicer than the one currently running.
+            older_data_dir_path = check_older_app_config(*app_config->orig_version(), true);
     } else {
-        check_older_app_config(Semver(), false);
+        // No AppConfig exists, fresh install. Always try to copy from an alternate location, don't make backup of the current configuration.
+        older_data_dir_path = check_older_app_config(Semver(), false);
     }
 
-    app_config->set("version", SLIC3R_VERSION);
-    app_config->save();
-
     SplashScreen* scrn = nullptr;
     if (app_config->get("show_splash_screen") == "1") {
         // make a bitmap with dark grey banner on the left side
@@ -1155,10 +1151,13 @@ bool GUI_App::on_init_inner()
     // just checking for existence of Slic3r::data_dir is not enough : it may be an empty directory
     // supplied as argument to --datadir; in that case we should still run the wizard
     preset_bundle->setup_directories();
-
     
-    if (m_init_app_config_from_older)
+    if (! older_data_dir_path.empty())
-        copy_older_config();
+        preset_bundle->copy_files(older_data_dir_path);
+
+    // Save PrusaSlicer.ini after possibly copying the config from the alternate location and after all the configs from the alternate location were copied.
+    app_config->set("version", SLIC3R_VERSION);
+    app_config->save();
 
     if (is_editor()) {
 #ifdef __WXMSW__ 

src/slic3r/GUI/GUI_App.hpp

@@ -341,8 +341,9 @@ public:
 private:
     bool            on_init_inner();
 	void            init_app_config();
-    bool            check_older_app_config(Semver current_version, bool backup);
+    // returns old config path to copy from if such exists,
-    void            copy_older_config();
+    // returns an empty string if such config path does not exists or if it cannot be loaded.
+    std::string     check_older_app_config(Semver current_version, bool backup);
     void            window_pos_save(wxTopLevelWindow* window, const std::string &name);
     void            window_pos_restore(wxTopLevelWindow* window, const std::string &name, bool default_maximized = false);
     void            window_pos_sanitize(wxTopLevelWindow* window);
@@ -351,10 +352,7 @@ private:
     bool            config_wizard_startup();
 	void            check_updates(const bool verbose);
 
-    bool                    m_init_app_config_from_older { false };
+    bool            m_datadir_redefined { false }; 
-    bool                    m_datadir_redefined { false }; 
-    std::string             m_older_data_dir_path;
-    boost::optional<Semver> m_last_config_version;
 };
 
 DECLARE_APP(GUI_App)