IOS to Chrome Cast drop outs after 40 minutes

Hi

Have been using Plex for a long time, around 10 years. Usually with a MAC base client and a Linux server.
For the last 3 years I have been running Plex Media Server on a Debian VM, Linux NAS, Running it either directly on a wired AppleTV, or casting from IOS iPhone 5s, and 6s to Chrome Cast v1 and now ChromeCast v2 as well. This setup has generally run well. I had this system playing non-stop for hours.
I now made the mistake and updating the IOS app. Consequently had to update the Server version as well.
Now I am lucky to be able to run it for around 40 minutes before it just stops. Usually I have to restart the IOS App, Chromecast to get control back. In some case restart the Media Server as well!
I have checked the if I am use secure connection: turned that off.
Checked the wireless channel and extenders. Adjusted them to the least congested channels.
Updated all.
None of this makes a difference at all.

Netflix and Stan to Chromecast works flawlessly. Spotify works flawlessly. It is just Plex that keeps dying.

Why is this happening? Can I provide logs?

I just turned off auto update checking. I checked the logs and there seems to some sort fo sync going on in the background, suspiciously close the the drop out time.

I really need some insight here please.
It is awfully frustrating, especially as I am paying for this.

Regards
Buggy

In addition:
I just discovered a error in the configuration. The /tmp directory was not accessible.
I am also using older generation Airport Extreme Router, with and Airport Express as an extender.

Running tests again…

Sorry,
One more addition - this may the the source for the problem…
Log Message:
[Chromecast] Player: Excessive buffering detected; unknown.

I keep having the Plex player on my AppleTV loose connection yet the AppleTV still has connection with Netflix, Hulu and others still working. Plex can not connect to server. Only restarting the AppleTV will resolve the Plex issue.

What Apple TV version?
I have a wired Apple TV 3, connect via PlexConnect “trailer app” method. See how that works.
Seeing of the the WiFi is the culprit…
Plex Server averge CPU 1.7% - definitely not an over loaded medias server…