This past winter, my last few batches the ABV dropped. New England hazy IPA to 2.5%, and the other Black IPA (Canadian dark ale) to 4.3%. It’s kind of gave me a sick feeling, after all the LOVE, work, I put into it.
I’ve brewed these 2 beers before and had great success. The Black was at 6.3%,the Hazy was at 6.7%. I let the fermentation go for several weeks. The basement was a bit low in temperature 64-67 degrees. The kit was knew, the yeast had a expiration date of 2028. I didn’t do a secondary fermentation vessel. I did strain the hops from the wart before fermenting.
I think you might be misreading your hydrometer. Once the sugar is in solution, it’s not going to disappear. The yeast will consume the sugar and generate CO2 and ethanol (and more, but that’s beyond this scope).
So what you’ll see on your hydrometer at first is a high Specific Gravity (SG) and Potential ABV%. As fermentation continues, the SG and Potential ABV% numbers will drop. That’s 100% the norm.
What I think is happening is you’re reading that Potential ABV% number as the “Actual ABV%”.
What matters for ABV is the original gravity (OG) and the final gravity (FG). The ABV is, roughly, equal to ABV % = (OG-FG)*133. Please provide more information - specifically your OG and FG and how you measure them. Refractometers don’t work after fermentation has started unless a correction for the alcohol content is applied.