Re: Replica won't connect to Master after server restart

[Peter Brawley]

So the replica was down for a time while the source kept churning. If the time is too long for replication to catch up, you won't like this but the usual remedy is a full replica restart (eg see "reset slave" at https://www.artfulsoftware.com/infotree/mysqltips.php).

Re debugging, if a 1062 error happens repeatedly with inserts on one table, on the master build a debugging stub round the insert, eg with a Trigger, that writes debugging info to another table, and track how that gets replicated.