Flow description says the following in the announcement thread
"Flow 3 (Tiers 1, 2 & 3)
Critical Strikes against #Control Defenders grant a Power Gain Buff, causing them to gain 45% of their Max Power over 15 seconds. If the Defender is Stunned, the Power Gain is Removed. Max: 3 Stacks."
Announcement thread:
https://forums.playcontestofchampions.com/en/discussion/174384/alliance-wars-season-15-defense-tactics-and-season-rewards-update#latestBut in practice, it is a passive power gain which cannot be nullified or staggered. Just confirming if it is a bug or if it was updated to be passive rather than a buff? Working as intended?