I had a few issues with my PMI-LHR-GLA, GLA-LHR-PMI getting cancelled, me rebooking for a day later, those getting cancelled, me rebooking for a week later and all of said flights appearing on MMB on the app and on ba.com.

When the newest flights were subsequently cancelled, myself still getting cancelled notification for previous flights I had already cancelled etc.. I phoned BA and the extremely helpful person on the phone said something along the lines of... "Wow, this re-ticketing looks a mess. Let me rebook you and clear it all up" and lo-and-behold, 10minutes later I have the same PNR with only one set of flights on all the BA sources (app and MMB online). It was beautiful.

No idea what wizardry she pulled but it was very much appreciated.