Please let me know what I can to to help this fixing. (testing, logging..)
I confirmed and fixed a bug in the code. In v0.20 and below, when the max ISO was reached, the exposure time will not increased further. I'll post an updated version shortly.
However, in general, I'd suggest putting the ISO adjustment at the end of the shutter range, like c_joerg suggests. This is what expected when I wrote the script. ISO usually has more impact on quality than exposure time, so you'd normally want to use shutter-only adjustment for as long as possible. There might be exceptions if you prioritize maintaining a steady interval or capturing moving subjects over quality.
Updated script is posted in the usual location.