The condition CVt = 0 was leading to a verification statement of 0 < 0, which caused an infinite loop.
The implemented safety measure would have broken this off after 2000 iterations of 10 000 Monte Carlo trials.
So, while it seemed to you that nothing was happening, BWStat was calculating frantically trying to improve precision.
Changing < to <= fixed the problem.
This special case of CVt = 0 also led to another programming issue, which I solved at the same time.
You can follow the details at https://github.com/remonds/Uncertainty-on-UTL/commit/b3778f6d509d2c2f859...

Is this solution satisfactory?

Thanks for your valuable reporting on this issue. BWStat is a program by and for occupational hygienists. Together we make it great.