Smartthings motion detectors extremely flaky

Smartthings/Aeotec IM6001-MTP are very unpredictable, They can be added without issue but they intermittently fail to report.

When same device is added to Smartthings hub, it's rock solid.

Distance from device to Hubitat ~ should work as it's on the approved device list.

This is probably due to whatever repeating device the ST motion sensor has chosen to route through. I rarely see an end device being a child device of the hub, generally they are always routing via a mains powered repeater. If they become a child device, they usually switch to another device as soon as the hub is rebooted, firmware updated, etc. You can download the Zigbee Map app from Hubitat Package Manager and see what device your sensor is routing through.
Mine is still sorting itself out after a UPS shutdown last night.