A possibility - sinuses - the congestion loosening up and raining to your throat (I've had sinus issues for decades. When they are plugged up, not an issue for my voice, but when they loosen, if I don't spit and snort rigorously, my voice goes. In the extreme, my throat gets infected and it's the old antibiotics routine again. I spent thousands on prescription powerful inhalents for decades until a nurse practitioner suggested a $50 oral regime that restored my sinuses to close to normal.)\

For 30 years, your experience was my norm. Dropping nhibitions about being }proper", honking nad snorting especially on the bike helped me a lot. Being "safe" in this COVID world is not a help to my throat and voice.

Ben