Quote from: Monsieur OUXX on Yesterday at 00:28:38EDIT 2 : I've reset all the settings to default (I changed the font, like I said before) but the issue is still there. I've recorded a video : https://www.mediafire.com/file/r4o3f4jitnx68cx/ags_troubleshooting.mp4/file
(WARNING: It will remain online only 3 days)
I noticed if I use AbortGame(""); then no window shows up while AbortGame("a message"); makes the window show up. I guess a window should show up even on empty messages. Edit: it looks like this is the cause of the error message not showing when AbortGame script call is with an empty string; I don't know why the null check there but one possibility could be to cause the script call to always be non null by using some default message if no message is passed like "The game has been aborted from script" or similar.
But I watched the video and the error message that disappears says there is a null-pointer error in line 379 that is being triggered at game_start, on your DebugGui.asc. But I don't know why it is disappearing fast in your case. I tried some null pointer errors here and they still appeared.
About debugging things, a new addition to AGS 4 that may be useful to you is there is a Watch Variables pane which can show your variables when you advance them step by step in the debugger.
The mentioned multi-monitor issue is this one, but it looks like something different from the video.