Is there any way to delete these "ghost" triggers, short of completely redoing the app?
This happens in all apps, if a device is deleted the trigger associated with that device goes away but if I add a new trigger to that app the trigger list appears as [blank] OR [new trigger]. No impact on functionality of course but an annoyance.
This shouldn't happen with "deleted trigger events." If that's what you mean, it's a different problem I haven't heard of before. If you mean "deleted trigger devices" (i.e., deleting a device used in an RM trigger), then that is a problem that has been posted about before. We've been told this is just a display issue and is harmless. If it still bothers you, there are two ways to around it, one of which is re-creating the rule. The other is to remove the device from all your triggers and actions before deleting the device, which is a good idea for all apps (I assume you mean "Rule Machine" when you say "all apps" above, by the way, though it's again a good idea for anything). You can see this in the "In use by" section on the device page, and it should also be in the popup before you remove the device itself. The only caveat with rules in particular is that if you clone or significantly modify an existing rule (working backwards and un-selecting devices before removing an action or trigger can usually still work around this, though), you may get some phantom "In use by" references for rules.
This is the most specific comment I can find from staff on this issue:
Again, nothing to be worried about after the fact, but there are ways to avoid or work around it. I'd recommend the former.