Posting this as it may point to a solution to other's experiencing this issue and maybe if the symptoms match and you feel you've exhausted all over avenues this may be worth a consideration.

(Excuse if the solution is already known and this is in effect a repeat post.)
(Please relocate on forums if in wrong area, unsure where it should of gone.)

Thanks.

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The Problem:
Disconnects occurring using wayshrines to port, loading into dungeons, exiting at end of dungeons, and bizarrely even using chat discussing tactics at a last boss of a dungeon. All the aforementioned could disconnect me from the game. This was not all the time and could happen once or twice an hour; sometimes more than others and more frequently recently. Relogging into the game before going into group content seemed to give a window I could normally get things completed before issues occurred.

Seemingly over the last few ESO upgrades/patches this appeared to be getting worse from a point some time ago, 9+ months perhaps at a guess, where the game worked seamlessly without these random disconnects.

As a note ESO was the only program this seemed to manifest itself in. I could stream and play other online games, download vids, movies for the TV etc,.. all fine.
My hardware had not changed; broadband is fast, pc high spec, etc.


A Suspicion
Reading posts I saw that ESO is meant for fixed rather than dynamic IPs. So a while back I checked this out,.. and mine (although not strictly fixed) but being with Virgin in the UK was always up and the IP address never changed.

In any case I registered to a well known site offering a fixed IP solution (free 30 day trial). Downloaded an app that monitored my IP address and notified if it changed. Strangely although my IP never changed at any point there were times when the app reported a change... strangely from the same IP address to the same IP address!

This raises suspicions so I had Virgin do connection tests over the wire who said the equipment was fine so at that point I didn't nail down the cause. As I say everything else still seemed to be working fine.


The Solution
After altering cabling in my house recently I seemed to have other issues with my broadband with it dropping speeds at times when using other equipment with cabling sharing the same trunking; and this shouldn’t be a problem with the quality of cabling in use. Anyway called an engineer out whom after about 20 seconds of testing, said 'that's your problem'!

Basically the power ratings being sent to the router from the exchange had dropped off. He went to the exchange, up the power ratings,.. and as if by magic,.. all is fixed!

So now... no disconnects on wayshrines, on porting, in group dungeons, etc. Once in game all is great! It's as if the issue of the last months have just evaporated.


To Conclude
Not a huge network techno so in layman’s terms...

So over some time the power ratings carrying my broadband signal had dropped sufficiently causing the router to lose its IP address at moments, which it pretty much immediately recovered (and kept the same IP address), but ESO doesn’t like 'dynamic' IPs and this seemed enough for it to lose its known session; or question it for security reasons perhaps! The game continued to work fine while riding about, fighting, performing general tasks in game.. until the next time I tried to port, enter a dungeon, etc. At that time game thought its connection had changed and dropped me out.

The period of time between these moments became more frequent over time and I suggest probably as the power ratings dropped off more. This seemingly made it appear each update of ESO was less stable than the one before. Strange no other apps showed symptoms,.. and strange I could continue to play as long as not porting, zoning, etc.