Since Beta 74, my default synced identity in the TeamSpeak 5 client changes after the daily PC boot. I use an identity 3 times, that means it has 3 different nicknames and every day the identity with the other nickname is selected again. On my other synchronized devices or TeamSpeak 3 clients the identity is not changed.
However, as soon as I restart my PC several times a day, I don’t have the problem.
There was no problem here before the update to Beta 74.