Well it seems it is outdated. Does the engine allows retrocompatibility for mods? I mean, that newer game/engine versions can run old mods. If not, that is a must do for sure.

I ran into this problem as well, same exact error message. Should I just restart my computer and try again?

This seems interesting! Another thought I had when watching the elephant videos (probably unrelated): All soldiers going back to idle at the same time when the elephant dies looks so abruptly, maybe there could be some randomness (like some cheering, some idle) or random delay.

They seem to have acquired them from Romans (possibly built their own with Roman engineers). https://penelope.uchicago.edu/thayer/e/roman/texts/cassius_dio/67*.html    https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Cassius_Dio/68*.html#9.5 Surviving evidence seems to point at bolt shooting light artillery rather than stone throwers. Page 86: https://whc.unesco.org/document/204934

I wonder if this could be solved, instead of removing how "solid" units are, by changing something else, like not reacting to repositioning so fast and simultaneously when close by (maybe hard to require), or being more permissive on supposed destinations if an obstacle is there (one can always reform after obstacles are removed if a specific formation is wanted, for which showing and shaping it by dragging the mouse at the destination like Rise of Nations and Total War would be useful, and has been asked).