Without knowing EXACTLY what the other steps you do are.
Or EXACTLY how the application is responding to these steps.
You're not likely to get an exact answer. Just potential pitfalls.
You say you repeatedly re-use the same controls. But we don't know what you do within each of these repeats. Or how the application state is changing as a result of your tests. Presume other things are also happening, not just constantly clicking on this same field/button? Much as I'd love to assume that everything stays the same, I can't. And neither should you!
It's kind of hard to say what's happening. But you posted the error yourself. Object not found. To which I've already mentioned two possible things that could be causing that.
But if it's happening intermittently (you say sometimes the first time you use it, sometimes the 11th) then it sounds more like a sync issue - ie. Something is usually ready at the point you try and use it, but not always. So you may need to verify that objects are in a ready state (an action on a previous object will often affect the state of other objects) before you attempt to use them.