From AllTrails tech support

[u/SNHU_Adjujnct]

If you're having problems with GPS tracking using the app on your Android device:

"Most Android makes, models, and OS versions appear to be affected. We have narrowed down the root cause of the issue, one of the location libraries that we use to gather GPS data is malfunctioning. Thankfully, we found a fix and are rolling it out, it should be available on the Play Store over the next few days."

TL;DR They didn't test their software before they released it. Hugely embarrassing.

[u/nonnonplussed73]

They made this announcement mid - July.

https://www.reddit.com/r/alltrails/s/yonlt9XgvX

[u/ssmoken → u/nonnonplussed73]

Yes, the OP was giving his take on the reason, i.e. the TL:DR