I now realize this mammoth macro is about (a conservative estimate) x100 times bigger than a normal macro

When I collapsed all blocks 1-by-1 (which took about 10 minutes

, as almost all were expanded probably so can search) it still crashed MD.
What about splitting it up? Maybe using 2 or 3 separate smaller macros might fix this issue. Your macro is 2.6 MB (which includes all the called action blocks), so try to maybe get under 1 MB per macro?. It seems that just under 1 MB the macro starts causing lagging issues in MD, and then some size above ~1 MB it starts crashing. I suspect it's related to the Action Block calls (as they need to be searched also, when in Macros screen). I suspect if you replaced all Action Block calls with Macro calls, this would fix this issue, but am not certain. Although it's not a practical solution, just my theory.