Hi Salva - this is very much looking like FG was getting overloaded on your system.
- Reduce the number of tokens you have in your tokens directory. Copy them to another location to allow you to do some testing with much less tokens - in the long run make them into FG token modules you can activate just when you need them.
- Only share player modules with the players. Do not share scenario modules with the players - this has a big impact on player side resource use. The GM should share individual scenario records when needed - and clear up sharing (remove the (p) or (s) icons) when no longer needed. As the GM don't keep modules you don't currently need open in the library.
- Reduce the resolution of your main maps/image that you plan to keep open.
After you've done all this, clear the player cache again before doing testing with a player instance connected.
Hopefully this will make a difference.