Ah sorry!
Just to test it I put one usage of an enum value into one Draw event which has live_enabled. It works for me. I don't get any errors on saving the file:
I'm using the latest stable GMS2 IDE and the lastest runtime. (2.2.4.459 / 2.2.4.366)
Yeah - it hasn't always been the case, I had it working just fine at the start, it's strange how it's started recently.
Although, my enum/macro init script is close to 900 lines now, as the project is very large. It shouldn't be the issue though - I'm trying to replicate with new project so I can establish more details around what could be causing it.