I use Thunderbird email on my Macs. I turned off Sort->Threaded which helped issues on my iPhone SE v2 (was problem on previous iPhone8). I no longer have to delete gmail account then re-add it. It seems to correct after a bit now. I think it has to do with how the mail in indexed for viewing. From long ago there was the notorious No Sender gmail bug on the Mail app.
That wasn't just an issue for Gmail. I had the No Sender bug with my iCloud Mail account, too. But, just add it to the list of issues, I guess...
¯\_(ツ)_/¯