Welcome to the community and thanks for posting!
This is a result of the changes SmartThings is making to their platform - specifically with how devices are defined. I suspect you’re still using a Groovy DTH for the Virtual Motion Detector which implemented custom commands for simulating motion. In the next-generation SmartThings world, those custom commands must be defined as part of a capability in order for them to be used by SmartApps.
SmartThings hasn’t announced a plan for transitioning their first-party Virtual Devices yet, but they did at least acknowledge it in yesterday’s update.
“We have received multiple inquiries regarding virtual devices, and have a plan in place to migrate individual devices. More information will be provided on this topic in a separate announcement.”
That being said, many community members are switching over to one of the many community-developed Edge Drivers that are available for virtual devices. Popular choices include:
Edit: I should also add that Voice Monkey seems to be a popular choice within the community for integrating with Alexa. I don’t personally use it, but it seems to have a pretty neat feature set and works well with the HTTP Actions in SharpTools (example).