[BUG] No hard fail when blocklist path is invalid

[Uinelj]

Describe the bug
When specifying a blocklist path that is invalid, error messages do appear but the process ends "normally", with a status=0.

Either:

1. Check path existence beforehand and stop if we have a problem with it,
2. Fail the whole pipeline if we encounter this error somewhere.

Moreover, blocklists are instantiated once per shard and it shouldn't be that way. Maybe make ut1-blocklists Send and/or Sync, and then use a shared blocklist. -> #74