I went to the Nether and spawns at another players base and I don't have permission along with not being able to access chat. I'm on SkyFactory 3 Node 2.
Normally you should be able to go TO the nether just fine, just make sure you use /is home or /home instead of the nether portal to get back again, or do you mean that you ended up in someone elses claim INSIDE the nether? If so I would suggest trying to contact whoever owns the claim and get them to unblock the portal so you can get out of it okay as most likely your portal will always try to connect to theirs.