Fermenter's Fizz Drops and gushers

I used some Fermenter’s Fizz Drops to bottle a couple of six packs before I kegged my last 2 homebrews. First one was an IPA that turned into gushers. Zero beer left in the bottles after they foamed over. Second was a Belgian Dubbel that foamed like soda pop, although it stayed in the glass and was pretty much drinkable. I caught a video of the Belgian. Any ideas what’s going wrong?

https://m.youtube.com/watch?v=EDc6yvGFi50

Three possibilities come to mind.
Starting with the most likely, I would guess that fermentation wasn’t done yet when you bottled the beers. Did you check with a hydrometer to make sure that the gravity stayed the same for at least two days before declaring it “done”? I don’t know how much brewing experience you have, but this is a common rookie mistake. If the level of foaming/overcarbonation is for bottles as you open them over a period of weeks, that is the likely cause.
Second possibility is your sanitation is not sufficient, and both batches were infected. If that is the case, the foaming/gushers should get more intense over time.
Third possibility is you used too many fizz drops per bottle. There should be instructions to tell what to use for 12 oz and 20 oz bottles. Read the label and check if you did it right.

Thanks. Of those 3, I think the final gravity readings may be my problem. I’m super careful about sanitation (using Star San) and I only used 1 fizz drop per 12 oz bottle. I didn’t take gravity readings for fear of contamination, so I just left the beer in the primary for 3 weeks for the IPA and 4 weeks for the Dubbel. I assumed that would be long enough, but maybe not.

Thanks again for the advice.

3-4 weeks should be long enough, unless the temperature was too low or there were other problems with the fermentation. A low pitch rate might cause the yeast to be slow, as could a pH that is out of whack, but if it is incomplete fermentation, it is best to just prevent it from happening again in the future by checking the FG before bottling.