Elements "Display rules" do not load/show properly

Hello there !

I've been trying a lot of things, and finally, need some help to track down what's going on.

Firstly, I've done all this and more:
• Clear your browser cache.
• Clear and deactivate any caching plugins (keep them deactivated if you need to post your topic).
• Use IE, Opera, Firefox
• If you have server caching in place, disable it.
• Deactivate your other plugins one by one to check for conflicts.
• Make sure you're using the latest version of the theme: 3.1.3
• Make sure you're using the latest version of GP Premium: 2.1.2

The issue is that when saving some Rules in a layout from the Elements tab, when coming back they all display "All pages".
I've seen that, if you rapidly go into the "Display Rules" you can see that the saved Rules are here, but some of them rapidly change to "All pages". What could cause that ?

An example in gif:
https://gfycat.com/neighboringleanbordercollie

I've seen that some other people had equivalent problem:
https://generatepress.com/forums/topic/element-hook-display-rules-does-not-handle-large-amounts-of-specified-pages/
https://generatepress.com/forums/topic/doesnt-save-hook-settings/
https://generatepress.com/forums/topic/layout-settings-dont-saved/