This is not an answer.
I do not know why, but I also lost access to all my Song Templates after the last upgrade to S1 220.127.116.11413 ( I am using Mac Big Sur 11.5)
I made a new one (it took a while) and saved it again...now no issues accessing that one. I primarily only use one template, so if you use many, this will really be a pain. This unexpected exercise gave me a chance to add a few new plug ins and a few other things I normally would tweak anyway (added VCAs, etc.).