I have the same problem, seems to have something to do with the “Team Settings & Inventory” device. It also seemed to only affect team 1, despite my device being set to affect all teams, and also seemed to only happen uploaded versions of my island. I was only using the device to give weapons on spawn, and I was able to work around it by deleting the device and using verse instead.
Agreed, changing sprint parms works randomly (mostly not), seriously bugged.
Any time I change a sprint parm and push changes, sprinting stops working completely. If I reset to default settings and close session and reopen works again.
To test further, I started a new island, only device is a player spawner. Messed with sprint settings and it breaks sprinting completely.