Hi FotisGeorgantas,
Thanks for using Apple Support Communities. To clarify, when videos stop playing in HD, how do you become aware that this has happened? For instance, do you notice the quality has changed? Are you able to change settings within any of the mentioned apps to adjust picture quality?
Since it sounds like this happens with multiple apps, start by trying these steps for one of the impacted apps. Guidance is from If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support.
1 Close and reopen the app
Force the app to close. Then open the app to see if it works as expected.
2 Restart your device
Restart your iPhone or restart your iPad. Then open the app to see if it works as expected.
3 Check for updates
To see if updates are available for the app, open the App Store, tap your profile icon, then scroll down to see if updates are available. If updates aren't available for the app, update the software on your iPhone or iPad.
4 Delete the app, then redownload it
Delete the app. When you do this, you might lose data that was stored in the app. Then redownload the app. Then check to see if the problem with the app is fixed.
If the same continues, does this happen on Wi-Fi, Cellular data or both? Do you notice a change in any other Internet-based apps such as Safari?
Cheers!
