I think the welding/spawn stacking bug has been fixed for nearly two years. I fixed an issue with how network ownership is assigned for characters and I haven’t seen the issue or any reports of it since then.
The fix was a bit speculative but it definitely seemed like a likely cause for spawn stacking issue where players could not move their characters at the time. The issue was that whenever a new part was created the network ownership was assigned to the closest character but the closeness was being calculated in the X and Z planes only. This would normally result in the network ownership for a character being assigned correctly or it would be re-assigned from another player after being assigned to them but occasionally if that players client was not responding you could be stuck above the spawn unable to move.
Now after the fix your client will always be assigned network ownership for your own character.