if it was a brand new fly wheel there shouldn't be a problem there, did they check/change the spiggot bearing??

I've known of a couple of 2 w/d's that the 4x bolts that hold the bell hsing to the box to be lose and that has caused a slight judder/vibration!

regarding the garage fitting it wrong cant see it tbh!

try another cable 1st as that's the cheapest option!