Hi,
you say in the past the flash was desoldered.
So have a look to this, to ident it is the original AMD flash device.
It must be a AM29F800BB.
Some tuner desolder the original flash and change it to a similar Intel or a AMD x800BT one.
So you can't flash it over OBD or in boot mode, because the internal flash procedure for this different devices wasn't the same.
In the last years I have seen a few of this.