There are two categories of stuck sensor problems.
The first one are the problems that can happen with any networked sensor working with any controller. There’s just a standard checklist of things that you run through. Here’s the FAQ on that:
The second ones are really weird things that only happen in a SmartThings environment, particularly the V2 hub environment, and seem to have to do with a failure to synchronize between the hub and the cloud account. They often involve multiple sensors at once, or randomly affect one of several sensors. These are a bear to track down, and you often have to get support involved.
So I recommend running through the checklist first, and then if that doesn’t fix the problems, contact support and get their help to look into the cloud.