@frostschutz,
I've attached a small debug log below. I started with a full reboot then read at normal speed for a few minutes. I also tried to manually note down when a next page button succeeded or failed:
10:56 fail
10:57 OK
10:59 fail
11:01 OK
11:03 OK
11:04 OK
11:06 fail
11:08 OK
11:10 OK
11:11 fail
debuglog.txt
A small observation, in case it helps. I had a feeling that when a next button failed, there was a brief sighting of an updated time/battery display AFTER the button press but BEFORE the page actually turned. But once the page turn had completed the display was blank.
ETA: I forgot to mention that there was no excessive battery drain overnight with the Forma on standby in a magnetic sleepcover. So definite progress on that front.