Mail app isn't sorting emails correctly on my Mac running Sequoia 15.4.1

Similar problem today in Sequoia 15.5 in sent log only. There are no visual filters or settings checked. The fix for some unknown reason was to right click on the message(s) that is out of order and select “ignore followup”. The message moves back to it’s normal place in date order. How “follow up” may have been activated is a mystery.

I use Apple's Mail app on my iPhone, and the Mail app on my MacBook. I've also noticed incoming emails displayed out of sequence, on both devices. But a more troubling problem this morning:

• Macbook incoming messages displayed correctly
• iPhone displays messages out of sequence: 12:05pm, then a message from 3 days ago, then a message from Dec 2023, then a message from 10:01am, etc
• what is troubling is that the sender of the Dec 2023 message also sent me a message at 11:07am today, which appears on the MacBook but not the iPhone. That new message is totally missing from the iPhone!

I'm using POP email instead of IMAP since it better meets my needs. There are other Mail problems as well (eg. if you create 2 different draft emails with exactly the same subject line, then the 1st email gets deleted from drafts). Apple, no excuse for such an obvious bug.

In my case it's only in the sent mail that it's not sorting. It is very unsettling to sent off and important email then when you go to check late it's not at the top of the sent list. At first it was just one days old email stuck at the top to the list, with the last update it's now to old emails stuck at that top of the list.

This is driving me absolutely stark raving mad. I hated the Follow Up feature (like I don't already keep track of things I need to follow up on myself), so I turned off "Follow Up Suggestions" in Settings / General. Or so I thought! Now my Sent folder is out of order and there's no indication why, except when I right click and see it's the Follow Up. Why can't I turn this thing off?? Apple, fix it!!

I have the same problem with Sequoia 15.6. I sort my inbox by date received (without using threads or filtering), and one email that isn't the latest keeps jumping to the bottom (where the latest should be), though if I re-sort, it goes back to the right place.

"Me too" -- in my case it started since I installed 15.6.1. I note that th there aren't any suggested solutions here: Does Apple ever *look* at these discussions?

Sequoia as a whole seems a bit shaky to me! Weird things keep happening: is it me (or rather my Mac)? Do I have a bug? It's an Intel 2019 27" iMac that I have.