I've just updated to Android 9 with build number 5.150 so this issue may be well known. The task switcher is very aggressive at clearing apps, much more aggressive than in Android 8.1. In 9 it often reduces the list to just 3 apps, whereas in 8.1 I normally had 5 or 6 there. This is very very frustrating for me as I have to go back to home and reload the app. It's even more difficult to understand why it does this because the apps are still active in the background providing notifications! The apps I use several times a day like web
browser, email, news and messaging are set as Active
or Working Set in the Standby Apps part of Developer Options, but this doesn't seem to affect the task switcher.
Is there any way to change how aggressive the task switcher is at clearing apps?