For the second error message, I found and fixed that problem but can't update the forge until Monday.
The first error message may be caused by one of the other problems I fixed, by something I didn't find, or maybe not by StepCounter at all. The error message is coming from the ruleset. Hopefully after I update forge, all your problems will disappear. But please let me know if they do not.
Speed setting to 0 seems unrelated to me. Probably that creature had some sort of root you didn't notice. If you're ever not sure why a creature has a speed max you don't expect, double-click their speed in either the CT or the character sheet. This will open their "speed window" and at the bottom, all effects affecting their speed will be listed. Also for the future, you can always turn movement limitation off to override a maxxed speed. You can use the image button of a chain to turn it off for everyone, or you can right-click and do it for an individual creature.

