When oinkmaster fails for some reason, the lock file is not being deleted any more and the CGI is locked indefinitely. You can recreate this by stopping unbound and running oinkmaster.
Patch has been sent to the development mailing list: https://patchwork.ipfire.org/patch/2260/
https://git.ipfire.org/?p=ipfire-2.x.git;a=commit;h=84227f7a1c1b5093c01a0cabd6160d82197ee04b