I was having similar issues. Turns out i had two other mods designed to "fix" the OG definitive on a rail mod installed.

Those who have issues with the security guard are probably people who have the "hazerd course on a rail fix!!" mod installed.

Those who are having A.I. Disabled issues probably also have the above mod OR the "Fixed Softlocks for The Definitive On a Rail" mod installed.

After unsubscribing from all three mods including this one and then resubscribing to this one. I started a new save at on a rail and had no issues. Loading my old save just caused a crash. However if you have a pre-on a rail save that should work too.

Presumably they aren't compatible with this version of TDOAR.

Also fair warning you'll still have to watch out for your cart getting destroyed. (I think)

This will not fix the issue where the two security guards vanish if they aren't killed when you kill the HECU grunts at the end of the level. I believe they are intended to die though so its not a huge loss (and it may be intended for them to vanish? (kill trigger???)).