I only lost 1 from Audi in 5 years, but I thought someone stole it. The same, as dust cap which magically disappeared at the hotel car park. Maybe both were just lost.
 
Mrs S's Leon has the same problem - although weirdly it's lasted 2 1/2 years without a problem, only to lose 4 from various wheels in the last 2 months. They're not being stolen, they definitely work loose.
 
I replaced the covers & bolts on my 2018 Leon FR with chrome bolts (£16.99 for 20). Look better and changing a wheel now much easier (& faster).
 
my ST 290 Black, which is five years old has just lost a couple of wheel nut covers. Thanks for the tip about pressure washing. now to check them all after each pressure wash. sighs