I was making hemp gorgets for clothcraft skills, and noticed that when I failed a synth, ingredients (up to 8x grass thread) were reported as lost in the log, but not actually lost. The stack with the "lost" ingredients was greyed out and unusable - until I zoned, at which point the full stack was usable again. Desynthing the gorget I could lose it, as usual.

Same issue with making glass fiber from 8 flint stones. Maybe it's an issue that occurs when you have 8 ingredients?