I have a dirigia with:
Arc coil, seismic bond, primed animal instinct, calculated shot, vacuum, synth deconstruct, manifold bond, momentous bond, regen.
In a mission as dante, when I cast 2 or 2+2+4, dirigia gains overguard as expected. However, the sentinel quickly loses overguard and the health buffs when I start killing enemies. In the time it takes the sentinel to lose overguard, neither it nor I take enough damage to lose overguard.
At one point I duplex bond was added to the above mod set, but I removed it, thinking it to be the cause of the bug. Removing duplex bond did not fix the loss of overguard.
This seems to trigger on every manifold bond proc
