Woohoo! @berkelmudez excellent find!…….I have been working on this problem for three days and you are right; any combo of other SMTP plugins with various other mailing plugins etc. just did not work. Postman SMTP plugin suggests the proper port to use (of which I tried prior, but had everything else wrong!) and fixed all notifications.
Note for others having this same problem: My system would only send out certain notifications regarding signups and email changes but anything dealing with activity in the BuddyPress system (why we USE BuddyPress!) it would not notify users of activity. Try the Postman SMTP plugin and get rid of the other stuff.
