I've had this Chromecast Audio for about two years and its aways been flaky with Spotify (it was OK with Google Music when I had a short trial).
Spotify is often stubborn to connect, sometimes I need to close the App to even be able to see the Chromecast device. Other times it will connect and then immediately drop out, randomly drop out during songs, or I'll lose volume control, or the playlist carries on streaming despite the Spotify app being paused or skipped to another track.
I've trawled the Google and Spotify forums, seems to be one of those issues where both companies just pretend they can't hear the users. The only workaround that sometimes sorted it out was going to the Google Home app and connecting via that, but often a side effect was lack of volume control. I've rebooted and factory reset the Chromecast, turned off the 5g wifi and restricted all devices to 2.5g, moved them around, changed phones etc.
So if this forum can't sort it out, all hope is lost! Its really annoying when you've put the stereo on a sleep timer and gone to bed (Stereo plays through various speakers via a switch) and it stops, or won't stop, or you can't turn it down, or it randomly decides to play Rihanna and I have to get out of bed and walk through the house to kill the stereo!
PS - everything is on the latest firmware
PPS - and now its on a mind of its own, phone is no longer in control...
Have experienced the failed connection sometimes, I usually just clear apps and retry and it goes away. Not sure about all the other problems you have though. Not much help really!
We've been experiencing similar and other issues - it's really a suboptimal setup. I've mitigated some of the problems by turning off Battery Saver for Spotify on Android. This doesn't fix the fundamental "can't see Chromecast audio on Devices Available"
[url= https://community.spotify.com/t5/Android/Chromecast-audio-drops-out/td-p/1559488 ]The other "fix" I've found is requesting a new test account from Spotify who will then release your email address and set you up a new account, I've found several threads about it on Spotify and CCA forums.[/url]
I've noticed the spotify app (on iphone) doesn't want to take control of the chromecast if something is already allegedly casting (not always true).
I have to go into google home and Stop Casting first. This is a recent phenomenon. Poor wifi can also lead to issues, unsurprisingly. I've got a second better placed wifi network which has made the devices more responsive, less error prone. BBC iplayer isn't great either, not super reliable and will often just drop/stop. Radioplayer is better for live.
I've got a first edition Chromcast. Never seen any of the issues you describe. but it does occasionally (like, every couple of months) need a reboot. Just pull the USB for a couple of seconds.
Buy a Gramofon?
[url= https://gramofon.com/ ]Gramofon[/url]
Mine was cutting out so I bought a ChromeCast Audio. I had the same problems you are experiencing.
It worked fine from my Android phone but was really flaky from my iPad.
I went back to the Gramofon and it's worked perfectly ever since, I think it just needed to cool down ( I work in IT so I'd tried rebooting it... 😆 )