You can’t block someone immediately after unblocking them because LinkedIn prioritizes over your convenience. Wait 48 hours, use mute in the meantime, or—if you’re a Premium user—nuke your interaction history.
While high, there is a general block limit. Some sources indicate issues after blocking 1,000 to 1,200 members. Official help documentation notes that users with over 2,000 blocks may experience difficulties managing their list and should contact the LinkedIn Help Center . Block a member - overview | LinkedIn Help You can’t block someone immediately after unblocking them