Yup, a few people have had this problem, myself included.
It starts by becoming difficult to get it into the slot, which is generally a sign that it’s about to split right down the middle. From my experience, the key only has a lifespan of about a year, give or take, if you’re carrying it around in your pocket full time..
Anyhow, mine split down the middle, but I managed to save the RFID chip inside, and it was fine to use just making sure I held it together until I got home, superglued the thing back together, and carried on. No signs of coming back apart yet, though I’ll bear in mind that the call centre seem happy to replace them at short notice, just in case…