Versions between android 4.1 and android 4.4 have a "fullscreen" switch in "gear" -> screen -> fullscreen. If the fullscreen checkbox is marked then logs would be awesome.
Fullscreen and other settings are stored in /sdcard/koreader/ and survive updates, so my guess is:
-a: you did a new install after cleaning old settings (or removed the folder all together)
-b: a new bug emerged on a legacy android version (4.0?) just because nobody can test that platform.
-c: a firmware update bumped api level, so a new option emerged in the menu.
AFAIK nothing was changed in the fullscreen behaviour since
https://github.com/koreader/android-...848f3a8511ce61 (june 2019) and the last modification for "really legacy devices" was
https://github.com/koreader/android-...0978337e8a574f in february