“Ask yourself how they could launch a billion-dollar satellite 🛰️ without checking its mirror?”
The Arrival 1996
The issue is not in a mirror. The problem is in a rotating diffraction grating that acts like a prism to select the wavelength of electromagnetic spectrum (all longer wavelength than visible light) that reaches the photodetectors. The grating mechanicals seem to have unexpected drag that slows down the rotation into the desired position. It could be from temperature variations (one side of satellite is very hot and the other side is very cold) or it could be a micro meteroite strike that damaged bearing surfaces. It could be from a speck of dust that shook loose during launch.
You can bet that they are working on a triage strategy to put the diffraction grating into the position that provides the greatest value (likely the longest wavelength IR setting) in the event the grating gets stuck.
Note that this is only the medium resolution sensor, so even if it completely failed there would still be other sensors that are very valuable.