I agree I need to update the WordPress and plugins, but I want to make of the website a full copy on an other domain I have and test all the updates first, since I have read that the new WP updates could break many things and I have edited many php files. Just been a little busy lately to do that.
But this does NOT explain why the same problem is on the fresh newly (2 days ago) installed WP has the same problem on a different domain.
Anyway as I suspected what would happen has happened, same as what happened before.
NOW after a few days of this problem all emails arrive instantly again.
It has now no use now for me to check the PHPMailer, since the problem is gone for now.
I do not use any non WP email forms or automated mailers, but it would be nice to see if that has the same problem.
Guess until next time, maybe some things just can not be expained and need to be accepted.
At least now I know of this problem, so when I need to send my new Files Forever customers there user/pwd, in addition of the automated email I will send them a manually sent copy just to be sure they got what they paid for.
If you would like to continue to investigate this, let me know and as soon as when it happens again I will update here or send you a PM (or support towards you personally, if that is possible)
Thank you for everything and best regards, Ron