It could be ZS. Or it could be bitrate vs bandwidth.

I am leaning to that actually. I have the streaming right now at 720p default, but that may need 2-3mb/s sustained? Vs if 5g falls back to 4g intermittently it may get as low as 1-2mb/s bandwidth.

That would explain why not every user is affected and why I haven't been able to replicate it. Just because network where I am is v good.

I will try some down sampling to 540p on a new library and see what happens.