I've got the reason :)
After stopping timer, I opened a dialog. After closing it, it was suppose to start the timer again. In my situation dialog wasn't closed yet when Timer started :) So now it's all good.
Another tip: for restarting timer I'm using dynamic invocation - it's exit should be named <Timer Id> and this Id should go to i.e. TimerId (like on picture above) using ancestor reference. That's for next timer stops.If you don't do it, Timer won't stop next time.
Thanks for advice!
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