Unity Culture changes when hitting play

I'm having a weird issue where I press play in the editor and my CurrentCulture is switching to something other than English (or invariant, I'm not sure what Unity thinks it's set to).

If in code I then set my culture back to invariant everything is fine. Unfortunately I can't figure out WHAT plugin might be changing it. In my own code there is only one place setting culture and it's setting it to invariant. If I remove that change then immediately my game turns to the other language.

This change is obvious because in the editor all values with a decimal change from 1.000 to 1,000

Even if I have an empty scene this is happening. Nothing but a default camera GameObject.

Any thoughts?

 

Further info. It doesn't seem to be on play but on script recompile too at this point.
Investigating the broken culture before setting to Invariant shows that it is AN invariant read-only culture... but the decimal separator is a comma (,) and the number group separator is a decimal mark (٬) also known as an upside down comma. What gives? This makes NO sense at all.