Loosing emails in version 7

I have been using Em Client Pro version 7.2.50008.0 for a few years and have had no reason to update it.
Over the years I have noticed that occasionally when its trying to link incoming emails from the same person together it looses some of the emails.
I have now had some incoming emails from the same person go missing completely from the local inbox with even the initial email in the series vanishing.
I am running Windows 10 Pro 64 bit version 21H2 build 19044.1706 and am using POP3 for incoming mail.
Was this a known problem with version 7 and would updating to version 8 or 9 be sure to fix the problem?

Over the years I have noticed that occasionally when its trying to link incoming emails from the same person together it looses some of the emails.

Can you do an example screenshot of “how you link incoming emails” where they then get lost. Blank out any personal details.