Are all the Gmail different threads (different Subject lines) or the same email from different senders? As you know, words can trigger filtering, such as "50% Off," so that could be the reason.
thank you so much for your reply. the gmails are from different people with totally different subject
I may onetime marked one gmail as spam.
As Latitia pointed out, if the sender is in your address book, it should be a safe sender. You may want to review that one Gmail block for any "bigger" rule, such as block from this domain. That's a stretch but worth a shot.
