Definitely not an interval issue then I'm afraid.
If you're willing to waste some five minutes installing/uninstalling, there should be a new nightly (afternoony?) with
https://github.com/koreader/android-...ncher/pull/170 included within a half hour.
It sounds similar to the problem described in
https://github.com/koreader/koreader/issues/5221
Edit: now available at
http://build.koreader.rocks/download...78_2019-08-20/