When I ALT+TAB out of rF2, say for Teamspeak, or a quick browser session, and can't go back to RF2, that is extremely annoying. This has been a long standing issue for many months now... If you also consider that leave/join taxes the dedicated server (or so I'm told), it really is an important problem to fix.
I always "alt+tabbed" rF2 since the first public build without any problem. Sometimes quite often when testing some car with Motec. But since I've changed my fried GTX 570 for a GTX 960, every now and then the sim freezes when doing that routine. In my case, as I'm generally testing with "locked" conditions, I don't mind restarting it. But I've had my share of "alt+tab CTDs" back on NR2003 that ruined a few online races for me. I know you feeling.
My case (Full screen mode): Pluggins on > Alt + Tab fails Pluggins off > Alt + Tab works fine So I did the maths...
Offline basically you can alt tab infinite times without a problem. Online you are out after a variable number of alt tabs. It can happen the first time or the fourth. Opening new software (motec, chrome, TS...) increases the chances of not being able to get back. Plugins do affect as said. With one of the versions of TV plugin I was never able to get back after an alt tab. This problem exists since rF1 so it is not likely to be solved ever. Not enough people complaining so no action will be taken. People offering windowed mode as a solution because they don't have fps drops doesn't help the issue being solved either.
with windowed, I use the win calculator or other program open ,or alt tab not work for me. since build 930 not work. in full, after some alt tabs I get an error with d3d9.dll. I only use trackmapPlugin V 0.96 . with the gtx560 and now with the gtx970 ,I have no problems with the fps using windowed.
All these plugins that use these DirectX proxy dlls (d3d9.dll) seem to be buggy. The plugin API in rF2 has new ways to get graphics into the sim without using proxies. This would probably produce more stable plugins. For example Gerald's TV plugin doesn't use a proxy. I think there is also some confusion with some of these plugins because people will delete the plugin but forget to also delete the d3d9.dll so the Alt+Tab problems will still be there even though in their eyes they have deleted the plugin.
Not sure which plugin you are referring to, but I have no plugin that requires or makes use of a proxy d3d9.dll.