I host my own server, and I’m not seeing anything blocking it from a mod_security standpoint nor do I see any php errors.
Under 6.0.4, if I deactivated the plugins and removed the marker xml files, reactivating the plugin would regenerate them. That does not happen with 6.0.5. Upgrading to 6.0.5 does not initially create the uploads/wp-google-maps/cache folder, however deactivating and reactivating does create the folders, but without the markers.
I did take a look at wpGoogleMaps.php and compared the 6.0.4 version to the 6.0.5 version.
Under 6.0.4 at line 201, you have:
if (!wpgmaps_check_permissions()) { wpgmaps_permission_warning(); } else { wpgmaps_update_all_xml_file(); }
That is missing in 6.0.5, and if I add it back into the 6.0.5 version, deactivating and reactivating now generates the markers.
So, I’m thinking when it upgrades and re-activates it’s not triggering the marker generation because it’s not being told to. Not sure why they weren’t being generated when I upgraded from 6.0.2 to 6.0.4 however. Maybe the wpgmaps_activate function is not being called at all during the upgrade process for the last few versions. That would explain the uploads/wp-google-maps/cache folders not be created when the plugin updates under version 6.0.5 and could explain the loss of the markers in the recent versions even though the generation code is in the function for wpgmaps_activate in 6.0.4 and earlier.
Looking further and comparing 6.0.2 to 6.0.4 I see that the function wpgmaps_update_db_check() at line 3783 has wpgmaps_update_all_xml_file() commented out in 6.0.4 and 6.0.5 where it was not in 6.0.2. Same at the top of the activate function, where wpgmaps_update_all_xml_file(); is commented out in 6.0.4 but not in 6.0.2.
So, I think these commented out lines / missing lines are the root of the upgrade issues.