I am having the same problem. When I try to update from Quotes & Exchange Rate Settings, it just says "unable to get rate from (stock name) to GBP. It's as though it's trying to convert a currency, except it's a stock. I think this also started when I upgraded as prompted
The Q&ER extension started returning this error with Australian stocks some weeks ago, this was with Moneydance 2019 as well, so I suspect that is may have nothing to do with the latest preview builds.
I can only suggest you look at using the Quote Loader extension instead.