Literally just bread yeast.
Its honestly just because I keep fucking around with it, adding tea which dilutes the abv then tossing more sugars in there to boost it back up again.
I'd figured it was mostly just bubbling due to offgassing but my hydrometer is still sinking a bit between each measurement.
Like i said, think i'll just finish the one up with a neutral spirit, backsweeten it, then manually offgas. Let the other one just go until it stops.