Hello Michael
So, as the TV was restarted to it´s original factory software the Apple TV app was unistalled and re-installed on the last public version. It did not helped.
On the intenet speed side, as tested directly on the tv i have 240 Mbps download and 21 Mbps upload. Using an ethernet cable lowers my download speeds to 95Mbps as the interface on the TV is only 10/100 (my router is gigabit)
The problem is worse playing apple tv + content for some weird reason. all other purchased movies ( titles with and without dolby vision and atmos) does have problems (out of sync subtiles, random crashes, stuttering) but are less frequent.
Trying to watch the second season of for all mankind, the app crashed so much on the season 1 recap that i had to:
Watch the recap and 10 seconds on my iphone and them restart the episode 1, as where i have left, on the TV.
Trying to move foward or backwards on the episode is a lottery and most of times leads to erros like: Episode not avaliable,
network not avaliable, try again. If the espisodes engages i don´t touch anything, maybe it plays all fine. I don´t even dare to pass the episode intro.
On the same TV, other popular streaming apps( N, A, D+,YT) works perfectly playing 4k, dolby vision and atmos, special functions and everthing.