Try this (no promises, and you may have tried it already):
1. Open disk utility
2. VERY IMPORTANT: go to the view menu and choose "show all devices".
3. Look on the left and choose the "topmost" line that represents the physical, external SSD
4. Try erasing it now. Any better?
One other thing to try:
1. Try erasing it to a PC format -- such as exFAT
2. If that works, "erase it back" to Mac format, APFS.