Found in an other forum an easy method to reproduce the problem.
disable the screen lock (it must be set to "None");
lock the phone and then unlock it;
lock and unlock it again.
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In the meantime, I found more users with this problem and a little solution that another user describes:
I can confirm I have the exact same issue since Android 9 with my Xperia xz1 compact.
I normally have no lockscreen options set. So when I wa...
There were lot of reports of glitchy phones after the Pie update.
The cure was a factory resetCan you please link a thread, where users told, that problem is solved after reset?
I have the same frozen display (since Android Pie), when turning d...