After installing and setting of adb, my smartphone worked flawlessly for more than a month via adb WiFi connection. Today, for some unknown reason, I was unable to pair my device via WiFi. I haven't updated anything on my comp and phone. I didn't enable/disable any additional features. I use the same android project. Reinstallation of adb did nothing. Pairing using QR-code and digit-code doesn't work at all, that's the reason I used adb. Troubleshoot Device Connections window doesn't help either.
Question: How can I pair my device to Android Studio (Koala) again via adb WiFi?
I finally found a solution to my problem. I connected the device via cable, enabled USB debugging and applied the Revoke USB debugging authorizations command. Turned off USB debug, turned on WiFi debug. After that, adb WiFi debugging has been working as expected. Here's a menu path:
Settings > Developer options > Revoke USB debugging authorizations