Strange random and instant disconnections

So, this has been happening since either the june 25th or june 30th hotfix, I randomly D/C with no error message (besides "connection lost"), it's instant with no lag and no sign that I'm about to D/C, I can re-connect instantly (although once or twice I get the "you are still logged in" message).
I'm playing on PS4, I don't lose connection to psn when these D/Cs occur.

Now here's the really strange bit....these D/Cs ONLY happen when I'm not in combat, they happen with high frequency the instant my party reaches a boss room within a duty or if hanging around in a boss room after beating the boss, but not if in combat at the time.
They happen with a high-ish frequency in my FC's house and workshop and with similar frequency in the lavender beds area in general, although they happen pretty much anywhere at all at a lower frequency.

I'm on a 60Mbps fibre optic connection, I normally use a cable to connect to my router but I've also tried using a wireless connection, it didn't make any difference.

I've tried all the usual fixes for lag/disconnections/etc. (port forward, DMZ, clear cache, turn it off and on again, hit it with a hammer, etc.)

Anyone got any ideas?

This happens to me too, and I'm not sure how to fix it.