Could it cause any problems if I run bisq on two devices with the same seed simultaneously?
It won’t cause any catastrophic issues. You will always be able to recover your funds with your seed. However, the app data files will differ between your installations and cause problems when listing trades and making/taking offers.
I think the recommendation is to only have one instance running. Backing up and moving app-data files when you need to switch machines. I’m sure somebody smarter than me will have more insight.
I guess I’ll go the safer route then, and set up a 2nd account on the other device.
Yeah, it is safer to not use anything from one instance on another at the same time.
You should not do that. On hte Bitcoin side there should not be any big issues but on P2P network side you cannot run 2 times the same onion address. The earlier started one would not be recognied anymore.