Inbox filters not applying or applying intermittently

I have been having problems with rejectng spam messages sent to my custom domain.

I have s catch-all active and somehow a random address got onto spam distribution lists.

My inbox rule is

email adress

Header part

To all

Is exactly

randomuser1@custom.domain

Reject with reason

"Message categorised as spam"

However, I keep receiving spam emails for randomuser1@custom.domain

It appears as though this rule occasionally works but then suddenly I get several mails per day bypassing the spam filter.

I can't see what I am doing wrong here and appreciate any help to solve this problem.

Thanks in advance