Troubleshooting cellular connectivity issues on the Sony Xperia XA2 with T-Mobile

I have done a couple of things to my Xperia XA2 to improve my LTE connection, and I'm not sure what will help you the most.

Reset wireless settings
I did this sometime around September when I was unable to make calls or send texts, but was able to use mobile data:

1. Open the Settings app
2. Go to System > Advanced > Reset options > Reset Wi-Fi, mobile & Bluetooth
3. Reset settings

Disable LTE Power Savings Feature
This feature was constantly causing my mobile connection to drop, resulting in my phone not being able to receive calls, texts. Sometimes I couldn't even make calls.

1. Open the Settings app
2. Enable Developer mode
   1. Go to About phone
   2. Scroll down to the bottom
   3. Tap on Build number 10 times
   4. Go back to main settings menu
3. Go to System > Advanced > Developer options
4. Scroll about halfway down the menu until you find the Networking section
5. Enable the Mobile data always active option.

How to set up Microsoft Authenticator on LineagOS without Google Play Services

I use the Microsoft Authenticator app on Android because it has one of the best interfaces for a MFA app, and it makes it easy to migrate to a new device. Well, normally it does anyways.

I recently install LineageOS w/ microG onto my Sony Xperia XA2 and had a heck of a time restoring my accounts in the Microsoft Authenticator app. It turns out that the app requires the Google Messaging Service (GMS) to add an MS account, and you need an MS account to restore your account backups. Of course it doesn't tell you any of this. No, it just gives you a generic error or sits there spinning its wheels forever.

Anyways, here's how to enable Microsoft Authenticator using microG:

1. Open the Settings app
2. Go to System > Advanced > microG Settings
3. Enable Google device registration
4. Enable Google Cloud Messaging
5. Add your Google account
     Don't worry, microG will still try its best to hide you from the all seeing eyes of Google.
6. If you have Microsoft Authenticator installed already:
   1. View App Info (long tap on the app icon)
   2. Clear Storage
7. Install Microsoft Authenticator if you don't already have it installed
8. Open Microsoft Authenticator
9. Tap skip a bunch of times until you see the "Restore" button at the bottom.
10. Tap the Restore button and log into your primary Microsoft account
11. Everything should restore now 

Note, that if you want to receive push notifications, such as Microsoft account login requests, you may need to check in to the microG push notification service called Firebase Cloud Messaging.

To test push notifications:

1. Open your microsoft account
2. While logging in, choose to use your Microsoft Authenticator app
3. If you don't get a notification, then you need to Check In to Firebase

To check in to Firebase Cloud Messaging:

1. Open the system phone app
2. dial  *#*#2432546#*#*
aka *#*#CHECKIN#*#*