Are the drive types properly set in CMOS Setup?
360 KB = 40 tracks, others are 80 tracks... if it's misconfigured, it's sure to fail while trying to seek beyond 40 tracks during POST.

Yes
It is configured as above:

A: = 1.44MB 3.5" floppy
B: = 360k 5.25" floppy

FD-55BR has more jumpers than just D0..D3
Post a photo of the board with jumpers, hopefully there's somebody with the same drive who can compare them...

Also, this stuff may be important - http://minuszerodegrees.net/diskette/5.25_flo … termination.jpg

I've found some photo of FD-55BR, trying to identify the terminator... is that the resistor pack near the 34-pin connector? Is it removable?

Could be a stupid (or poorly pirated) BIOS that does not perform the seek correctly on 40-track drives. By the time these motherboards came out everybody pretty much moved to 3.5" floppy drives, and even those were about to become obsolete. While I've never seen a BIOS that would not properly support 360k drives, it's not completly out of the question.

Deunan wrote on 2022-03-06, 23:10:

Could be a stupid (or poorly pirated) BIOS that does not perform the seek correctly on 40-track drives. By the time these motherboards came out everybody pretty much moved to 3.5" floppy drives, and even those were about to become obsolete. While I've never seen a BIOS that would not properly support 360k drives, it's not completly out of the question.

Ahh I agree ! Specially because: "If I remove the "floppy seek on post" on bios, it works well".
Yes !! sounds like a quirk in the BIOS, wonder if same would happen if a 720k 3.5" drive.

but OP doesn't want to disable floppy seek since he likes the sound it makes.