Update:
After following John's suggestion and updating Horde, same connection issue continued.
Also as per Jean-Philippe suggestion, I looked at logs and could not see anything out of ordinary.
To me it looked like it might be a PHP issue. I had PHP-SCL contrib installed for a while now, but only changed PHP versions per i-Bay as needed. This time I have decided to change setting for http server, not just i-Bay
The setting was set to default, so I changed it to PHP71
It has been over a week and no connection issues so far.
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