Subtitles out-of-sync on ATV4

I have PMS running on CentOS 7 on a Mac mini (mid 2011).

I have the following clients:
Apple TV4 (wired)
iPhone 7 (wifi)
MBP 2016 (macOS 10.12.6) (wifi)
Android Galaxy Tab A 10 (wifi)

They’re all running the latest versions of Plex.

On the ATV4 subtitles, both embedded and external (downloaded by SZ), are out-of-sync when the “Burn Subtitles” setting is set to “Automatic”.
On all the other clients they are in sync (and set to “Automatic”).

However, if I change the ATV4 setting to “Always” - they are in sync.

Any idea what’s going on? What is it “Automatic” actually does - and why doesn’t it work on the ATV4? I’m mostly curious and want to understand what’s going on.

PMS and the ATV4 are connected to the same switch (Netgear GS105 1Gbe switch) and the house router is a Asus RT-N66U.

I hear you, subtitles are a real issue and always have been. PLEX has been rather relaxed at trying to address this issue for many many years. If I recall (maybe wrong) bit many years ago they gave you the ability to speed up or slow down the dialog to match the subtitles, this has since gone the way of the dodo.

Why I cannot help you, all I can say is, do not expect a reply, or fix from PLEX. They love building new features into PLEX, but do not do a great job of fixing long standing issues.

Personally, I wish they would stop adding and just concentrate on fixing all the issues across the software. Once that is done, then add new features.

Don’t get me wrong, I love using PLEX but the constant upgrades and new features is overwhelming. Just fix the current issues, that is all a lot of ask.

Subtitles actually work fine in most instances. SZ is really good.

But, like I said, I’m trying to understand what’s going on.