FIX: pseudo-random "Syncing disabled" on Samsung Android 10 release (as of early Jan 2020)

[Rich Belgard]

I've been using K-9 on every Android phone since Nexus 1.  

I've never had problems with syncing my polled email, even with the first (December) release of Samsung's Android 10.  But...

With the January Android 10 update for my Samsung Galaxy S10e (and I suspect all Sammy phones), I noticed that K-9 would not poll for email, and display "Syncing disabled' even though Auto Sync was set on, and I had either or both of Wifi and Mobile data connections. (I have K-9's "Network" setting to "Background sync "When Auto-sync is set", although it also randomly didn't sync when set to "Always")

I discovered that this seemingly is because this Android release incorporates even more battery power management techniques.  After a few minutes of non-use, K9 apparently was being put to sleep/doze/snooze/whatever.  However, I could not figure (easily) how to set K9 to NEVER SLEEP.

THE FIX:

On the Galaxy S10e (and probably your Android 10 Samsung phone):

Settings | Apps 

<scroll to K-9 Mail>

Touch "Battery"

Set "Optimize battery usage" to "Not optimized"

[possibly] "Allow background activity" slider to on (mine is now greyed out, probably because I'm now "not optimized").

That's it.  Now, K-9 syncs when it is supposed to, and doesn't when it isn't.