I updated my app at the end of last month without issue. Today I added a batch of new puzzles and did an Android build to send out to my testers. I loaded the app onto my test device via the ADB and the app crashed moments after launch. No runtime error, nothing in the log- the app just disappeared right after the splash screen showed up and I got a popup saying, "Word Search World Traveler has stopped \n [refresh symbol] Open app again". Reopening the app just produced the same result.
After restarting my testing device, I did a bunch of ruling-things-out testing: sideloading old .apks (worked), building from archived versions of the app (didn't work), building from a different computer (didn't work), building demo apps that didn't have any plugins (worked), etc. After coming to the conclusion that it was something plugin related, I started turning plugins off and on until I could get the app to launch. At the end of the day, commenting out Firebase allowed the app to run successfully from a new build.
I've noticed AdMob touting enhanced Firebase integration recently, so my guess is that they changed the SDK recently, but that's based on no evidence other that what I've noticed out of the corner of my eye when I'm checking my AdMob dashboard.
If anyone has any insight into this, I'd be curious to hear it.
I used Corona build 2019.3480 for both today's work and the functional build from last month. No changes to the build.settings or the Google Services files.