reasons i dont like doing defense/interception in pub groups especially lith. can't count the amount of times an equinox shows up in a lith defense and just kills everything as it spawns then we end up with around 5 reactant. you'd think that after the first couple of rounds of 0 reactant they'd clue in.
as for capture, just try to get as much as possible BEFORE you capture. i've yet to run into this issue in a capture mission that switches but i get my reactant as quickly as possible then just zoom to end.
fissures should just keep spawning enemies no matter what until extraction. at the very least code it in so that it only triggers if someone doesn't have 10 reactant yet.