Messages randomly missing

Hi, I have been using K9 Mail for years but lately my provider has, from what I can tell, upgraded their mail server, and now I am only getting some messages showing up, and others are just randomly missing.

I haven’t worked out what is making them not appear. They are appearing on other mail clients. In today’s list I am seeing perhaps half of the messages, with the missing ones interspersed between them.

They are running an Exchange server of some kind I believe, and always have been, but they have an upgraded version now as I understand.

Any settings or other ideas on what could make this reliable? I’m loath to switch to another app after using this one for so many years, but this isn’t workable at the moment. I have uninstalled and reinstalled. The same messages seem to be missing all the time.

Thanks in advance