[Android Q&A, Help & Troubleshooting] nikwin:
Some very weird things started happening on my phone earlier today. It's a Nexus 5X, running 8.0 Oreo, with the October security patch. I'm not rooted and I'm careful about what I install. The phone is fairly new, from this summer.

I will begin with describing what I did in the hours before this started. I can think of two things that possibly could have started it:

1) Two of my Facebook contacts sent malicious links to me an hour before. It looked like Youtube videos but was not. I did NOT open any of these links, knowing directly they were harmful (not sure if you can be affected by just receiving them, not clicking on them?). I received them in the Messenger Lite application (an official app from Facebook with scaled-down functionality).

2) A few hours before the Facebook links, I sideloaded an APK containing the new Pixel Launcher. I got the APK from Android Police/APK Mirror.

Can't attach links, but Google for: Hands-on with the updated Pixel Launcher, including the new Pixel 2 features [APK Download]

The APK was working fine and nothing seemed odd with it (I used the launcher for a few hours). As long as Android Police know what they uploaded, this shouldn't be the cause for my problems. I bet on Facebook Messenger instead. (People that click such malware links typically get their Facebook accounts hacked, however my account seems fine and my account didn't spam others with the same link. I did not change password or did anything else to "recover" my account yet).

So what happened after this on my phone?

Here is the first thing I noticed. I open Play Store to install updates. It turns out I have one update pending, it's called BankID. This is a major Swedish app used by nearly every smartphone user in the country, and it's for signing into government websites, bank websites, insurance company websites, and much more. When I click update in Play Store two things happen almost instantly:

1) Six pictures are downloaded from Messenger Lite to my phone. That makes no sense, how could clicking a button in Google Play trigger something to happen in Messenger Lite? In fact I tried it three times, with the same behavior every time. (Well, actually opening the Messenger Lite photo album, there are only photos there I already downloaded, so nothing new seems to be added there - but the photos were probably re-downloaded I believe).

2) The BankID update downloads to 100 % (the downloading takes a little longer than expected), then it halts and does nothing, i.e. it's not installing. No error message, it just stops there. I can choose to abort and try again, which I do three times or more, with exactly the same behavior.

Also, I now notice Play Protect hasn't run for two days, but when I try to run it, it seems to be down. After ~30 seconds of scanning it says "App verification temporarily down". "App verification temporarily down" could very well be connected with the halted update I just described? It still says it hasn't run for two days after this.

When I experiment, I notice other things that are very weird indeed.

1) Notifications in Gmail, Snapchat and possibly other apps aren't coming through. By opening the apps, I can sync manually.

2) When I move a file to a new folder using the Downloads app (Files app, stock one) I get a error message saying the move operation failed. This also triggered the photo notifications from Messenger Lite (same behavior as described above, with six photos). However, after a while the moved pictures are indeed in the right folder, even though the error message saying otherwise.

3) After some time I remove "app data" for the Google Play app. When I open it after that, there are now three app updates pending (e.g. Google Wifi also). But the same behavior occurs, when I try to download one or all of them, I get the Messenger photo notifications and the updates halt at 100 % without installing. So the BankID app - which could be targeted by attackers for obvious reasons - could just be a coincidence. It could have happened with any app I suppose, this was the only one pending right then. But still, why couldn't Play Store detect other pending app updates until I refreshed it the way I did? Was Play Store blocked from connecting to Google (or forced to connect to some other server, perhaps?).

What did I do after all of this?

I uninstalled three apps:

-Facebook Lite

-Facebook Messenger Lite

-Pixel Launcher APK

However the uninstall process was very odd. A process called "Package Installer" had a notification saying "Uninstalling Lite" and "Uninstalling Messenger Lite". It didn't seem to be working, it was stuck after some time. I restarted my phone and the apps seem to be gone now, at least they aren't listed in Settings --> Apps. So the uninstall process was successful I suppose, even though it didn't seem to work.

After I restarted my phone I also noticed:

-When I install Messenger Lite from Play Store now, it's easy to uninstall it the way it should be - in mere seconds.

-When I open Play Store, updates are now installing fine. Play Protect is also scanning fine now.

Everything looks back to normal now. But I'm not trusting my device. I'm gonna factory reset it. Before I do, I wonder:

-Can I feel safe the wipe would erase whatever malware I might have had on the phone?

-Is there something I could do to let us know what caused this? Upload a log here somehow?

The only piece of advice I have received as of now is: "Try restarting in safe mode, installing some AV software, and generally looking for suspicious processes." I haven't done that yet, would it still be a good thing to do? Must I install AV software before rebooting into safe mode, or could I install it directly from safe mode? (App suggestions, AV software?).

Usually I'm very careful and security-minded. I haven't had something like this happen before. So I'm very intrigued and mad about this. I'm gonna change my Google account and Facebook account passwords later on I think (I already have 2-factor authentication enabled).

One last thing: When I install Pixel Launcher on my non-rooted phone, it's not running as a system app if my understanding is correct. (At least it shouldn't be). But none the less, when I wanted to uninstall it I had to go into Settings --> Apps and tap "Show system apps" to find it in the list. Is that normal? Perhaps it doesn't mean anything, I just want to know.

Thanks for your advice in advance. Anything else to add? What should I do know? All you might have to say is appreciated.