Really bad smell when first turn on AC

[iDiesel]

Issue was fixed during last service they replaced the pollen filter
Working fine again - especially after these last few days, woah it’s been hot!!!

[FastMitch]

I had the exact same problem with my 2015 BMW X1. The problem ended up being a blocked condensation drainage hose that caused water to build and eventually soak the polled filters causing them to go mouldy and hence that smell you get.

Common trick from Dealers to generate 'work' is to block the condensation drainage hose during a service job

Once they block the hose, the whole system fills with moisture and stays there when the engine is turned off

This creates mold and bacteria that then causes a rank smell that infects the whole AC system

Clearing the drain hose may require some hot days to dry out the system before the smell disapates as well as replacing the cabin filter

Last SUV dealer wanted to charge me a 'flush and cleaning fee' where they would put a 'cleaning' gas through the system. Cost $200

[Ozsko]

Common trick from Dealers to generate 'work' is to block the condensation drainage hose during a service job

That sounds like an urban myth to me. I have had decades of involvement at dealer level and have never seen this done.