By the way, as when disabling the plugins, i could not distinguish between core and third party once and have disabled them all. How can i re-enable core plugins ?

You don't need to deactivate Elgg core aka bundled plugins.

You can use 'Bundled' filter on the 'Plugins' page to find out the core plugins.

Hi Fathi, can you please check and share your error log for that "Check for Updates" plugin. If there is some issue with the plugin then I would want to fix that. Also please share your elgg version (4.0 or 4.1)

event is managed by Event manager https://elgg.org/plugins/736695 but don't know if these two files are both generated by this plugin or only the fullcalendar file

find ./ -type f -iname *fullcalendar*

./mod/event_manager/vendor/bower-asset/fullcalendar/dist/fullcalendar.print.css
./mod/event_manager/vendor/bower-asset/fullcalendar/dist/fullcalendar.js
./mod/event_manager/vendor/bower-asset/fullcalendar/dist/fullcalendar.css
./mod/event_manager/vendor/bower-asset/fullcalendar/dist/fullcalendar.min.css
./mod/event_manager/vendor/bower-asset/fullcalendar/dist/fullcalendar.min.js

For the second file, the only occurrences i have in my server of files named leaflet are from glpi and its plugins, in its own installation path.

Assume, you've activated Event manager v12.4 not v13.0.

Or..?

leaflet.js script is loaded from unpkg.com/leaflet@1.2.0/dist/leaflet.js

So, try to check this URL in the browser's devtools (Ctrl+Shift+I)

Also, run 'Flush the caches' and check your issues again.

I created a fulcalendar symlink to fullcalendar.js

Why? You don't need to do anything; just activate Event manager.

If you're using any 3rd party installed plugins then disable them and check again.