Beamng keeps reverting back to windowed mode

Good Morning all,

Just as the title says, the game keeps reverting back to windowed mode. I'll press Alt-Enter, it goes back to full screen, and then a few seconds later back to windowed without any input from me. Any ideas?

 

I had this issue a few years ago, so i'm speaking from a vague memory here, but some programs can cause this if running in the background, The only one i can remember that caused me any issue was TeamViewer remote desktop client thing, so if you have that i suggest closing that down, if not, any other similar programs could cause it. Hope it helps