Strange behavior of Format Date in shortcuts

I have a shortcut I use to create new Jekyll blog posts on my iPhone and iPad. It works great most of the time. However… sometimes, the format date command interprets MM as minutes instead of the two digit month code. Here’s my format string:

yyyy-MM-dd HH:mm:ss ZZZZZ

What’s very odd about this is that it will work properly 90% of the time. Then it gets in a state where it is substituting the current minute in the MM field. Repeated runs of the script show that it matches the current minute. Then the next day it works fine. Here’s a snapshot of the code in shortcuts as well:

Is there something obvious that I’m doing wrong here, or is this some sort of intermittent bug?