Soundstage gone

try reversing the polarity on one speaker.  if the Soundstage goes back to normal, your cartridge is miswired.

FWIW, while I’m not sure about Teo_Audio’s terms I can assure you that some products do need to "break in" to reach their normal performance. I don’t think a long period is necessary to hear the promise of great things to come but from my experience I will judge nothing that hasn’t been operating at least 24 hours. Nothing. I usually find the product ’dark’ and closed in and after some time passes the mid’s and highs start to appear. Probably the best thing for you to do at this point in time is to be patient and see what happens. "Soundstaging" lives in the mids and highs which are often late developing.

If after 24 operating hours (I like to actually use the product, not just leaving it on)  you note no difference then perhaps its time to press your dealer for some kind of resolution.

BTW, I assume you have other sources plugged in, have you checked them to insure the line stage is operating properly? I assume that you have, but.....

If you have a mono button on the amp play a mono record, if when you press the mono button the sound nearly disappears you have the cartridge leads crossed on one channel, if it doesn’t its in polarity, the background noise might reduces if it’s an old mono disc but not the music.

From what I read, OP has no phono equalization. Going from cartridge into MC gain stage, then into line level. Totally bypassing the necessary RIAA equalization stage. Yea, that would sound exactly as he describes!

Wolfie62: the Linn Urika is an mc only phono stage and has the RIIA equalization. Is intended to go straight into a line input without any additional stage. It's also designed to work with the Linn Kandid cartridge but works very well with other mc cartridges.
I'm quite surprised by most of the comments above, no knowledge at all of the products...
OP, your dealer needs to visit you at home and fix the problem (this is what I will do with my customers).