12 Speed shifting issues

Hi, can anyone help me try to fix my poor shifting issues on my 12 speed SLX derailleur. When shifting down the gears (smallest to largest cog) the chain skips before shifting unless I get lucky and shift just as the chain hits the right tooth. This only happens when shifting into the largest 2 cogs and in the middle of the cassette.

The hanger appears straight and I have played around with all the adjustment screws. I have started again from scratch following the Shimano instructions and the only thing that seems to help is reducing the cable tension but then I can’t shift from the 2nd to 3rd smallest cags.

The bike is only 4 weeks old (nukeproof reactor) and has only done about 50 miles.

I did take it back to my LBS and I was told that it is normal and should quieten down with more use, does this sound right?

Any suggestions on what the issue might be?

Thanks