Strike Gust & Grand Wave Deband/Shifta Buff Duration?

How long are these supposed to stay?

I get very inconsistent duration ranging from ~5 sec to ~60 sec. What determine their duration?

It is determined by the number of pulses that hit you. Each pulse gives you 15 seconds of Shifta/Deband, and since the Bouncer PAs gives you a fully charged Shifta/Deband, you get 4 pulses. If you leave the range of the Shifta/Deband or activate another Support Tech (like Resta) before all the pulses hit you, you don't get the full 60 seconds.