Explain the L3-37 Revive mechanic at work here

OP didn't specify how long it took. I merely read their description of the battle and it fits what Vandor does. It's the only explanation for L3 reviving more than once, as much as it may not perfectly fit your list of restrictions.

OP also didn't list what each enemy did on their respective turns. Bad timing on OP's part could result in Vandor having a buff/being prepared as L3 died. Not out of the realm of possibility, again.