I haven't been able to replicate it deliberately, and I'm not sure how I keep doing it; but every time I load up I get one of these numbers stuck on my screen from either the dig tool or the cancel tool. And they persist until reloading.
Steps to Reproduce
With the dig tool selected, drag over several tiles, release, and then click again. Or with Cancel tool, drag over several buildings
This issue has not been confirmed by a developer yet.