Very stange indeed. It's what I've done at first with no results.
I created some global variable, some buttons while waiting for a reply... And after your obvious answer, I changed this tile and redid the same... works !
It was too easy...
I paused the rule I made (to increase the volume), played with different mini's (to understand why I was so #"£##"% : censored) and now the sliders behave like in the beginning : no variations.
The slider reflects the volume level IF I change it with my Google Home on my phone. But nothing happend when I slide the slider. And more amazing, the slider doesn't reflect the volume setting: see that the slider position is not reflecting the volume setting...
(example of Mini-Living: volume set @ 90% but placed in about 25%)
Do you have the same problem that everyone else does with your minis becoming unresponsive using the Chromecast beta integration? If so, that's your problem. Try sending a notification to one of the minis that's "out of sync" . The dashboard is not the problem here. It's the device. The dashboard is just displaying the data and it works 100% for me (and many other people).
Yes and No. I can't say the Chromecast beta integration is defective because a trick I made in a quick (rule and tiles) is 100% reliable. If the Chromecast Beta is the culprit, I could have similar problems whatever the rules used. Am I wrong here ?
I don't know what you are asking. You wanted to know how to control the volume from a dashboard. That's how you do it. Is that not working you're saying? Can you control the volume from the Edit device page?
Also, either pause or disable whatever else you have for the mini. Did you ever stop to think that THAT might be what's screwing up what is supposed to work.
I paused them all. And tested from the beginning the behavior of my google mini's through the built-in volume slider tile. And it works so-so. sometimes yes, sometimes no. And no apps to interfere.
So I build a rule with a virtual volume slider and it seems working since all the time. No explanations yet. But it works...