quick response - Are the 2 different monitors on different GPUs?
if yes, search this forum on that exact issue for a solution [sorry, not an issue I've had, so I don't recall the exact details, I just recall reading about issue]
Yes indeed. 2 different graphics cards used for the individual screens' input. The onboard one and a slightly broken but usually better one by amd. If using multiple GPUs while screencapping multiple screens on one computer is a known problem, i'd like to encourage the obs team to improve that. the software is really great already, but that was something i got really confused about for quite some time
If you did the search, you'd come across the technical reasons for the issue. I could easily be wrong (as my add-in GPU can handle all the monitors I need, so not something I've dealt with), but the resolution might require OS level changes... or a level of App change that isn't reasonable for an FOSS package without a paid service/support offering/plan. Again, I could be wrong.. but my recollection is that this isn't an easy issue. your own research can provide you more details