Hmm, I'm getting that exact same crash, except I'm not using Mayasuran Navy at all. I'm having a much harder time repeating it, though.
Earlier, we were having consistent issues with the Energon Bazooka because its projectiles are meant to use the same arming code as phase mines, but Alex changed the name of the missiletype of it from phase_mine to phase_charge (Alex messed with mines this patch). It's likely something similar here, if the Didymoi mines were based on an existing vanilla missiletype. From the GuidedProximityFuseAI entry, I'm guessing it's the same issue here.
(Frustratingly, I'm now getting a similar crash in a different combat, but I cannot find the culprit since it's not invoking a FuseAI, just the MissileAI, and in other combats all the suspects seem to behave.)