I keep tinkering with it and apparently the problem (at least in my case) has to do with inherited events. Here's a recording of the issue: https://i.imgur.com/VbL0ejX.mp4
If I save changes to the event it's reflected correctly on the debug output message, unless "event_inherited()" is in the code. Just in case I tried with "event_inherited()" both before and after the GMLive function, since I didn't know if it had to be in front or before, but in both cases the same result occurs. As soon as I comment out "event_inherited()" and resave the event code, GMLive works again.
As a workaround I put "event_inherited()" in a custom 1 line script called "inherit_parent()" and that seemed to do it. I can have the GMLive call and my "inherit_parent()" script on the same event code.