Wing Mirror assembly is buggy with the components it consumes. What seems to happen is if you are installing any mirror that isn’t standard, it consumes all standard mirrors currently on the stockpile. If you have predictive stock control applied to the assembly, it doesn’t consume the mirrors at the start of assembly but at the end, not sure if that bit helps. The assembly then throws an “Insufficient Resources” status and halts assembly until more standard mirrors arrive. I’ve tested this with Folding, Heated and Folding Heated Wingmirrors’ all with the same result.
I’ve done numerous scenarios to reproduce this bug also experimenting with predictive stock control and one thing I noticed was the bug kicked on or about the 8th car to go through the assembly line. After that 8th car, the assembly was bugged until removed and replaced. The bug kicks in again though.
I made a quick video showing the bug. https://www.youtube.com/watch?v=VFo8aUnVrjs&feature=youtu.be