Yep, just checked and that happens on my side too. Also, I just tried slowly scrubbing maxstretch and when I hit a certain value near where it looks like the spine scales to zero, Maya froze. So I am guessing there is some division-by-zero problem or similar.
Maya 2018.5 - Windows 10 - mGear 3.0.3 - spine_ik_01 module.
Also on spine_C0_root
you have some stretch profile options. As a quick fix, you might be able to find better values that don’t hit that singularity. But when I was scrubbing those attributes while the spine was over-stretched, again Maya froze. Editing those attributes when the spine isn’t stretched doesn’t seem to cause any problems for me.