I thought these seemed off (sometimes they would reset if people left before a virus was uploaded) and I can confirm after a very solid 4 person attempt tonight that the generators are resetting ahead of schedule, while there is still time left. I've noticed this in 3 and 4 person attempts when everyone jumps platforms.
Additionally, respawn of the Borg seems to happen MUCH faster than it did about a month ago.
I'd argue that this needs to be reasonably completeable by three players because, when auto-teamed, new members cannot be invited at the boss phase. Adding pressure at the end just encourages people to quit who cannot be replaced.
As a design note, IMHO, that means I think challenge should be frontloaded very early into STFs, which should get easier but more team oriented as they progress. I know it seems backwards but I'll guarantee your designers it works better with a queue system.
In any case, though, the Borg respawn rate has DEFINITELY increased and the generators are frequently resetting ahead of their timers.