My guess is part went towards series C PS conversion to completion, part went towards series D PS conversion and part of them were sold to generate cash via the ATM. No matter how you slice it, it still represents >$10M on the credit side of FCEL's books (that apparently wont be disclosed in Q2 numbers)
I'm also a bit hesitant to even say that "part went towards series C conversion to completion".
The last sentence of pg 3 from NT-10Q "partially offset by Series C preferred stock deemed contributions of $1.6 million for the three month period ended April 30, 2019 compared to Series C preferred stock deemed dividends of $4.2 million for the three month period ended April 30, 2018."
I've yet to fully decipher that "deemed contributions of $1.6M" but it certainly implies series C PS are fully converted.