Perhaps it was mentioned already but I missed it. Are the tracks that are stretching zinc alloy or polypropylene types.
I've actually seen both types stretch. That poly tracks stretch with respect to time doesn't surprise but zinc alloy is a bit more complicated.
I've read that Asian die casters a Zamak alloy which isn't as resistant to stretching as the US standard alloy. You can look it up
if you are curious. Perhaps Erik can research which alloys their suppliers are using; I'd be curious.
Jerry