Same for me. Re-installed the app and same result.
HOWEVER, it seems to be linked to the “live” feature, cause when I use the “replay” function (I go back 30 seconds), all streaming goes fine. But the moment I watch live television again, the de-sync gets worse hour after hour. It becomes unusable.
I do not have this problem with Teleboy, Wilmaa or Zatoo so it must be the Swisscom app that is faulty. So fix it please!