PS4 cannot connect to Plex via app

Hey all

having an issue connecting both my and my sons PS4’s to Plex

an error screen comes up stating

**Unable to connect to “My DS name”

We tried to connect to:- “DS IP”. You are signed in as Draig88

The selected server cannot be reached securely. An insecure connection may be possible. You can change settings>… and try again**

I’ve since done this and still no luck. I’ve also gone through the checklist on the page at help.plex.tv/noserver

Ensure you have the current version of Plex Media Server installed - Yes
Ensure that Plex Media Server is actually actively running - Yes
Verify that your Server is listed on your Devices page - Yes (both server and both PS4's)
Disable any VPN on your computer or router - Checked and no VPN present
Disable any proxies being used on your computer or router - Checked and none found
Make sure you aren't requiring secure connections on the server while using an app that doesn't support them (see below) - Done as far as I can tell

Further checks

When both your Plex app and Plex Media Server are on the same local network:

Make sure both the Server and app are on the same subnet of the network - Yes

If your app is not on the same network as your Plex Media Server:

Ensure that Remote Access has been successfully enabled for the Server - Yes

Further info

Plex Media Server (version 0.9.16.3.1840 - cece46d) is running on Synology DS212J version with Static ip (PS4’s are on dynamic IPs)
Router is a BT Smarthub (this is recent addition after my old BiPac Billion expired) and port forwarding seems to be set correctly (PC works fine as does iPad and to a lesser degree the old PS3, although it returns the error 2006 occasionally)
All PS4’s can see and access the Plex Server via “Media Player” but cannot connect via the app
The app locks up after giving the error message and I cannot retry, get out or close app without pressing PS button and restarting the PS4
Everything has been rebooted after any change but still no luck

Help!

I have the exact same problem. The only difference is that the server runs on a Qnap 451+.

I have the same problem aswell, everything worked fine until the latest server update, then it broke