Welcome to the Audi Owners Club !
Good to have you onboard
Hello Graham,
Could be barking up wrong trees, but starting to work once it’s part way open could be significant.
Potential trouble spot ( but your vehicle may not be old enough) is the fracturing of wires in the flexible harness section twixt tailgate and body. When the tailgate is partly open the wires may just touch enough to make contact. Worth an eliminating-look at.
Of course, it could just be a fault tailgate lock.
Kind regards,
Gareth.