After an apparent stall by a CRJ at FL390 back in April, the FAA has imposed altitude restrictions on SkyWest CRJs, apparently all variants. The FL280 restriction on the CRJ200 is particularly onerous from an operational standpoint.
The original incident sounds like a coffin corner stall.
FAA Imposes Safety Limits on SkyWest After April Incident - Bloomberg Business
A Bumpier, Lower Ride for SkyWest