You can try with sh nlcache reset command, together with updall.

updall -r names.nsf
drop all
dbcache flush
sh nlcache reset

First of all, thanks Vedran for reaching out. I did what you mentioned, just waiting for someone to send an email to the "GroupA". I'll get back to you once I see something.

And there's something I forgot to mention in my earlier post. This issue was present for sometime , even when we were running 8.5.3 FP6. In between, there were quite a number of restarts which should clear the cache wherever applicable.

Check document properties for the size of the document - if it's close to 30K or so -

Create a second group, move the last 10 users or so to the second group, then add the second group as a member of the first.

There's a 32K limit on the size of text fields - this shows up as an issue quite often with large groups.

You can create a meeting entry in your calendar, include Group A, and press F9.  Then confirm that the two members are present or missing from the list under Required.