I faced the same error screen as #93.
Mobile App works for me too.

Checking-in via mobile app, I had no chance to put my FFP number on my record.
I had put them when I reserved seats in advance but now my record lost my FFP number.
I try to add it online they just return error as follows.

Unfortunately we were unable to record your Frequent Flyer number in your check in record. Please use the Add/Update Frequent Flyer function, or present your membership card at the Airport check In counter.

I used Add/Update Frequent Flyer function
I'm afraid I'm treated as non-elite flyer... I have OW Sapphire!

Edit: I confirmed my mobile BP shows I have no tier.