Tahoe didn't come up after staging storage node reboot: `builtins.IndexError: list index out of range`

Tahoe doesn't start with

2022-09-23T11:21:52+0000 [-] Unable to write to plugin cache /nix/store/7nkwz2ic8rvc6q60y18mjld0hbkhzp76-python3-3.9.13-env/lib/python3.9/site-packages/twisted/plugins/dropin.cache: error number 30

Of course it can't write there. Why does it try? Why did it work before?