i need two left feet

Something is happening. There is a particular treadmill at the gym that I prefer. When I am on it, my right foot toebox slides out from under me. But only on that treadmill. I hve inspected both shoe and treadmill and cannot find out why this is, but I don't like it one bit. I ran on the crap-dracula treadmill for a few miles instead and bailed on it to do weight-training instead. Weird.