Errors with Outlook Auto Complete

Over the last 2 -3 days, emails sent to a group of people are received OK but the display in the To field of the copy I have on my Sent folder and the display on the recipients To field in the received email is wrong.
For example, I send an email and Auto Complete fills in -
John <[email protected]>; Bill <[email protected]; Joan <[email protected]>
John, Bill and Joan all get the email but in their version of it, in the To field, it reads John <[email protected]>;
Mary <[email protected]> and Fred <[email protected] address3>
My copy in the Sent folder has the same thing in the To field,

John, Bill and Joan all get the email but Mary and Fred (who are listed in my Autocomplete file) do not, so could be worse!!

All 5 people's addresses are in my AutoCompete file Stream_Autocomplete ....... dat and are correct.
I have looked at the file using NK2Edit (the updated version that works with the latest Outlook and Windows). I have deleted the original file and created a new one. But while addresses are correctly Autocompleted, the display in the To field after sending is corrupted as above.

Q1 - No - I used NK2Edit.
Q2 - Yes
Q3 / 4 - I think the problem is related to when I send an email to several people.

I am probably saying what you know but for those who don't know, I'll add it.
There is a program called NK2Edit (https://www.nirsoft.net/utils/outlook_nk2_edit.html) which allows direct edit of the AutoComplete file. This file used to be a stand alone file but in later versions was incorporated into the Outlook PST file. So for a while NK2 no longer worked. It was updated and this is what it says now about it can be found at https://www.nirsoft.net/utils/outloo...e_changes.html