If I upgrade past 2.4.2.143 on my C5 legacy dashboard none of my virtual thermostats work. I can attempt to change between modes such as cool or heat to off or vice versa they aren't registered.
If you bring up developer console (usually with F12), does the JavaScript tab show any errors?
If there are no errors, can you switch to Network tab, issues a command, and post these two screenshots?
I've seen occasional reports of this issue, but can't reproduce it locally.
Also, could you please PM me you hub's id? I'll check the engineering logs.
So I have legacy dashboards that didn't need to have devices assigned specifically to them. Once I added the devices to the legacy dashboards the items started to work again.