I saw some of the posts and have rebooted the Smartthings hub as that worked for one person. Also some about clearing the cache. Will test again.
Not sure what you mean by ‘multiple definitions for the same device’. I each Nest Protect added to Smartthings with the NST Manager device handler and it is ‘in use by’ your OpenHabAppV2 and Action Tiles v6. In the OpenHabAppV2 settings on the Groovy IDE under Event Subscriptions, all the right channels (smoke, battery, carbonMonoxide, powerSource) are associated with an inputHandler and the OpenHabDevice is associated with openhabMessageHandler. So it looks OK to me, to the level of my knowledge (not great).
It feels like it is almost working so will persevere.