Euph, yes your bike was indeed faultless during torrential rain.

Could be a bad batch of leads, coils, EFI, sensor reading wrong, could be EFI itself, a question for a real engineer. Needs a BMW or Bosch engineer from Germany or Austria, I'm sure they'd find the problem in five minutes with the correct apparatus.

If it was my bike I'd try:

1. Make sure I had a Japanese manufactured NGK spark plug of the correct rating and gap measurement.
2. Buy a new internationally known brand battery and long charged it properly before I used it.
3. Change the lead to an NGK.
4. Try running Shell 97 octane.
5. Try changing the fuel filter if possible.
6. Try chevron techron fuel system cleaner or BG 44K
7. Try rewiring electrical system better
8. Try an aftermarket air filter and muffler to see if increased air flow actually helps.

after that I'm stumped, and would clearly be a Jialing company issue.