If you share (or previously shared) a LinkedIn Recruiter account with the person, LinkedIn may restrict blocking or require notification to the account admin.
The lockout lasts If you unblocked them at 3:00 PM on a Tuesday, you can re-block them at 3:01 PM on Thursday. If you share (or previously shared) a LinkedIn
Since you can’t block them, here are the exclusive workarounds that actually function: If you share (or previously shared) a LinkedIn