You may be aware but if not 
Warning - If you have aftermarket valve dust caps fitted to your vehicles I suggest you check
them
As my daughter had a set of fancy red square ones fitted on her car. I called at local garage today to check her tyre pressures but could not remove valve cap tried to force it and the whole valve pulled out of wheel managed to jam it back in before to much air lost I then drove to local tyre depot
They told me that valve caps had got hot and expanded and they had got welded on to the valve thread and are impossible to remove. 
Told me they get them in all the time and showed me a bucket full of welded valves
Had to have all 4 valves renewed at a cost of £20. 
As the caps were on the car when she bought can’t say where they were purchased.
SO IF YOU HAVE THEM BEST CHECK THEM
The real problem is the cap corrode onto the valves. It’s a process called galvanic corrosion.
It happens when dissimilar metals react to each other, in this case aluminium and brass.
You can prevent it by smearing a small amount of silicon grease or something similar to the valve threads before screwing the cap on.
Or stick to plastic caps!!
I think it’s more corrosion that causes it, aluminium valve cap fitted to a brass (?) valve.
A smear of copper grease can help prevent it.
I bought some fancy metal caps on eBay. Not fitted them yet but the thread is a plastic insert so hopefully these won’t have the same problems.
The solution is very simple. CHECK YOUR TYRE PRESSURES ON A REGULAR BASIS. It is not rocket science, the reliance on ‘technology’ to take care of simple checks is a sign of the times. Analogue is best!!
Yes, I’ve heard about metal dust caps giving nightmares. I too wondered if someone checked their tyre pressures every fortnight or so, maybe they might be fine, and maybe it’s users leaving them for months that might be the issue. Given I never really trust the likes of Pete404Rocket or Mad4itMike or CowgirlDenise_456 or say Scoobygotya1, or whoever, on the internet to really provide trustworthy info on their alleged use (yeah, I check them 4X a day bruv etc etc), I never risked it. Maybe an idea is to go around the car and just give each of them a twiddle once a week say. Takes what, 60 seconds.
The problem lies with the types of metal involved. Aluminium will react with brass and fuse together. (Galvanic corrosion) that’s why often the aluminium valve caps have a plastic coating inside. Personally I would avoid aluminium caps altogether.
Just to add to this I recently had problems inflating the tyres on one of my vehicles and could not work out why. At first I thought it was my inflator but I found out it was down to my caps. The caps had a white rubber seal inside them which had come out of all the caps and stuck inside the valves stopping the air going into the tyre. Seals removed and all was well.
I had a slight panic on the way to the rally today. Bombing down the M40 and the low tyre pressure warning lit up and bleeped at me, great I thought. All tyre pressures checked yesterday before the trip. They are new tyres, valves etc.
Pressures checked again at the next services, as I thought all bob on. It’s the car throwing a wobble, I reset it and alls well.
All cars seem to do it, my FK8 & current S3 have done the same thing.