I have transnational replication on PROD. suddenly we are getting consistency errors in replication because of update statement (not for delete and not for insert).

update command working as Delete/insert pair(deferred update) @ subscriber .

we made only one change recently , we dropped clustered index on that big table1 as part of troubleshooting prospective. we are getting these error on table1 as delete conflicted with reference constraint

solution : everyone says "DBCC TRACEON (8207, -1)"

but Why this is happening all of sudden? we didn't add any new unique constraints on this table1.