First priority would be to establish if there now is a general problem with your device not having mobile data or Wi-Fi connection. Browser working, email send and receive all the things you would use more frequently.
This links discusses the fastboot commands around changing slot – https://xdaforums.com/t/can-i-change-the-boot-slot-from-fastboot-with-a-command.3977207/
First (without commitment) you can try
fastboot getvar current-slot
I belive this will help you establish you have effective Fastboot communication.