@Hokoshiさん,
Thanks for providing detailed logs and screenshots. You can follow the steps provided in the Solution section before doing Step 2~4 to solve your problem.
Root Cause
Basically, your issue is caused by the B&T original firmware being transferred to board flash via Over-The-Air (OTA) method, which causes your micropython firmware unable to be loaded.
If you are interested to explore more, you may refer to the guide here.
Solution
You may erase the B&T original firmware using AmebaD image tool following the steps introduced in another forum article: [Resources] BW16 Troubleshooting Guide.
どうもありがとうございました。