SamyGO

You can`t do it w/o risk.
I wouldn`t suggest you to use FFB once more, because you probably get same situation.
Try manual way. here is no safe way left. FFB was the safest...

I think you needed to have ExLink cable.
Than you can watch what is wrong with new firmware.
You also needed to update your u-boot code to avoid bricking in any way.
Than you could try FFB tool or flashing by hand without risk

apolo7, can you give some logs from USB you used for upgrade with FFB (if not deleted)?
U-boot, kernel and fnw were restored because you copied required images to USB. I just need logs to confirm that.
I do not remember if switching to "februar" firmware deletes partitions, i made some tests few months ago and as i remember, u-boot and TOP debug menu were working, just enter to shell was limited by firmware - just ctrl+c did drop to console. Only installation deletes 2,4 and changes 5 partition, switching not.
So you need to solder/buy cable and to check if you able get either to u-boot or debug menu.

So we can see from log that images for accessing Top debug menu and u-boot are flashed successfully. Now to be 100% insured, you need Ex-Link cable.

Yes, errors are quite normal.
Now, try u-boot and TOP debug menu. Just confirm if you able to get in.