Hi guys,
New to the forum but not to MiSTer - I've had mine for over 2 years now and I love it.
I upgraded to an RMC MiSTer Multisystem board when they first released and it's been running fine. I haven't changed anything on the hardware side of things since then.
However just yesterday I started running into a problem. Have a look at the attached screenshots.
The images are from the Sega Mega Drive/Genesis core but the same thing happens on every console core that I've tried (I haven't tried any Arcade or Computer cores since it first happened so it may or may not affect them too). It appears to be intermittent but happens often enough for it to prevent me using the MiSTer most of the time.
It happened after running the update_all script so I'm not sure if it's a bug or new incompatibility that's been introduced somewhere, perhaps in MiSTer Main? I tried using a default MiSTer.ini just in case it was related to a bad .ini but the problem occurs when using the fresh, default .ini too. I've attached the MiSTer.ini that I'm currently using just in case though.
I've also run the update_all script again but that hasn't made a difference.
In the interest of providing as much info as possible I'm outputting via HDMI to a 4K LG TV. I use 1920x1080@60Hz but run most cores in PAL mode as I'm from the UK and my muscle memory is trained on games running at 50Hz as opposed to the slightly faster NTSC 60Hz. Not sure if this is related to the problem or not but it's always seemed to be fine doing it this way until now.
Also I did change some of the video processing options on some (but not all) of the affected cores just prior to this issue occuring - however I'm assuming that's unrelated as changing the setting back to what they were hasn't stopped the issue. Also some cores that exibit this issue haven't had any of their config options changed at all recently.
I'm officially stumped! 
I'm hoping this is a bug/software issue rather than a hardware issue as I'll not be able to afford to replace the DE10 Nano at current prices 
Does anyone know what might be causing this or how I might go about fixing it?
Thanks.