There's a chance that the left channel had dropped out/been somehow disconnected somewhere in the audio chain, perhaps going into the on-air processor (e.g. Optimod, Omnia) or anywhere after the main program output of the on-air console. A lot of it depends on how CHIN feeds the 91.9 transmitter and where the processor is; if they're feeding the transmitter via an IP connection or by old-fashioned 15 kHz telco lines, the processor would need to be at the transmitter site so that the composite signal and an RDS signal, if applicable, can go into the transmitter - most FM transmitters are fed via the composite input on a BNC connector. At the studio end, from the on-air console, there would be, at the very least, the AlertReady decoder (Sage Digital ENDEC unit) and the studio side of the feed to the transmitter.

Apologies for the tech jargon... I often worked with this kind of stuff in my previous years in radio.