I don't have a repro (I'll try to see if I can isolate something) but I'm on v0.27.0 and started running into this recently (perhaps from v0.26.0, in a couple colocated repos):
$ jj
Internal error: Unexpected error from backend
Caused by:
1: The lock for the packed-ref file could not be obtained
2: The lock for resource '[...]/.git/packed-refs' could not be obtained after 1.00s after 16 attempt(s). The lockfile at '[...]/.git/packed-refs.lock' might need manual deletion.
I don't have a repro (I'll try to see if I can isolate something) but I'm on v0.27.0 and started running into this recently (perhaps from v0.26.0, in a couple colocated repos):