Amiga 4000 doesn't recognize GVP A2000-HC+8

Yes.
But do you need it there for the A4000 to see the card, or just to use it?

[Kronos]

AFAIR the GVP did use Z2-DMA just like the A2091, which won't work
with Z3 (atleast not if you don't have any memory in the Z2-area).

There was a firmware-replacement (GURU-ROM) by Ralph Babel (?)
that fixed that problem.

So might I asked you to check whats printed on the ROMs in your card ?

Yes.
But do you need it there for the A4000 to see the card, or just to use it?

The GVP ROM:
V4.5       1992
DF24

When I just got the card, second hand, It worked more or less. I used a zip drive on it.

[Kronos]

Did you put that undocumented jumper back into it's original position ?

If yes: You fried your board !

If no: Do it, and if it is back to it's former behaviour, try to find someone
with an A2000. If it works there, get the new ROMs (or you fried your A4k).
Iif it doesn't work: You fried your card.