Welcome
Ah yes, 'specialists'...
Such a similar story.
We had our 2001 V70XC's gearbox rebuilt by a specialist.
They had it back and redid it twice due to shuddering. Then they tried to say it was the viscous coupling.
In the end I fixed it myself by replacing the fluid they had used with Smith and Allen's JWS3309. After I had done the second drain and fill the shuddering went, never to return, I carried on and put the full 20 litres through to be sure.
Should have done the whole damn job myself.
For the fairly minimal cost of the fluid, a simple drain and fill every service isn't a bad idea.