Sounds like you are either missing a spacer between the bearing inner races or the existing one has collapsed & effectively shortened the distance.
The center spacer prevents bearing side loading, which you seem to have. The shop may have lost the spacer or didn't notice it being damaged. The side loaded bearings will fail in short order due to stresses they were never designed for, even if greased.
Rear hub bearing replacement is a simple job, well within the capabilities of the home tinkerer. Were the replacement bearings rubber shielded? Wheel bearing replacement is the kind of stuff that is best done by the owner, as the owner is pretty much the only guy that has a vested interest in it being done right; it's a job that doesn't take special tooling.
Pull the wheel off and see if the spacer is still in there. There shouldn't be any side slop between it and the bearings.
https://www.hitchcocksmotorcycles.com/partsbook-pages/5292 - this shows an "exploded" view.
https://accessories.hitchcocksmotorcycles.com/41886?qty=1&continue_url=https%3A%2F%2Fwww.hitchcocksmotorcycles.com%2Fpartsbook-pages%2F5292This shows the spacer itself. It is pretty thin wall item, I'm thinking it deformed or rusted away.
2018 Himalayan - PART No. 587501 ; SPACER ASSEMBLY - REAR HUB ; £5.03
Good Hunting and report back what you find - ACR -