LinkedIn’s safety algorithms treat rapid block/unblock actions as suspicious behavior (similar to spamming or bot activity). The 48-hour cooldown acts as a on relationship changes, protecting both parties from automated harassment scripts.
You had a fight with a former coworker, blocked them, then felt guilty three months later. You unblocked them out of politeness. The next morning, they spammed you with sales pitches. Now you can't block them. You are stuck for 48 hours.