If EA FC 27 custom tactics are not saving correctly, start by keeping only your preferred custom tactic assigned. Check your active formation before entering a match, and test a fresh setup if the problem continues.
There is no confirmed universal fix documented in the official patch notes for every reported version of this issue.
Still having the bug? The most useful detail is whether your formation resets when you reopen the tactics menu or whether your players move into the wrong positions only when the match starts.
