Sometimes a garment cannot be seamed with the yarn it was knitted with, try a buttonhole thread instead. That’s what I did when seaming the Inversion wrap/jacket from brooklyntweed worked in LOFT. That stuff seems to break when looking at it. Seams resolved with the lovely buttonhole thread that Alabama Chanin recommends for sewing their cotton jersey fabrics. Fabulosity and these seams won’t break.