Are these third party plug-ins? If so, what are they? Also, what are your sources (pixel dimensions, codec)?
First thing to try is to reset your fcp preferences.
This only happens with the plugins that came with FCP. And only some of them.
It was working fine originally.
This happens on any imported video or jpg. The videos are usually from an iPhone or YouTube. So they are 1920 X 1080 or smaller.
BTW, if you look at the screen shot of my Graphics Display info it says "no display connected". Don't know why it says that. I have 2 cards an both have displays connected that are working fine. Don't know if that has anything to do with this problem.
iphone's usally record h264 quicktimes which are NOT suitable for editing in fcp. They should be converted to an fcp friendly format like prores before importing into fcp. Do a search here and you'll see many many posts about this. And although h264 files are not suitable for editing in fcp, they will sometimes work. Just not a smart idea.
FCP has also had problems with 2 display cards. Most display cards allow 2 monitors so the second display card is probably unnecessary.