GMap is unable to save the marker bundle public://js/gmap_markers.js

When clearing the cache with Drush, I repeatedly keep seeing this error.

GMap is unable to save the marker bundle, so the markers will not work. Please check file system permissions of the public://js/gmap_markers.js!

.

I checked the permissions for over a dozen times just to make sure it's not me, but they are good. The same as all other files on public:// and those settings work.

Also I seems that every entity with a map attached to it, loads terribly slow. Some Views pages with event nodes on them take for over a minute (used to be 2-3 seconds). Something since 2.10 that could have caused this?

I deliberately did not post this in #2282939: SLOW loading a GMAP page → because this issue appeared only after updating from 2.10 and as such cannot be related to the other issue (reported under 2.9).