I have missed multiple messages from the chromecast app because the Q has 20 entries stuck.
First of all is there a fix in the works?
Second of all, if not, then what is everyone using to get a spoken message to come through when it needs to come through? I can't afford Sonos so is there an alternative way. One of these days I am going to miss a very important message!
No sure what you are using to get your messages with chromecast, but I use Google Minis and all four work perfectly.
I can’t speak for chrome cast.
For tts I use either the fully kiosk browser running on my tablet, my amazon echos or my sonos that I just got.
However, if the message is that important I would not just rely on tts. Too many things can go wrong like the issue with the chrome cast or my Alexa cookie not renewing or even the sonos volume being too low to even hear it. Even my fire tablet gets N update every now and then and can’t log back in automatically.
For really important things I have it sent to me multiple ways at once. Email, push, and tts. I can even have it call my phone using IFTTT. That way if one method fails I still get the message assuming it’s not an internet outage.
I use the cast-web-api for my Google home devices. It allows you to use the broadcast feature so it doesn't interrupt anything and it never fails me. You can also use the cast feature to use native HE tts services (Amazon Polly) if you prefer. Just need an RPi to run the node server.
I was having at least one Google/Nest device drop every day until I started sending an 'Initialize' to them. I use my 'Follow Me' app with the Chromecast beta. It sends an 'Initialize' every 4 minutes to my Google/Nest devices (home, mini's and hubs). Since I started doing that, I never have a problem with them. If you don't need/want a full app, you could setup a rule in RM to send the 'initialize' too. I've tried a lot of different times but 4 minutes seems to work the best.
I threw this together in about 15 minutes, figured there would be more that need it. Hope it helps! 
The most reliable TTS has been in my Echos using this method, until such time that contact sensors are directly supported to trigger routines.
Except for the occasional hiccup due to SmartThings cloud, this just works, day in, day out. Door announcements, laundry, and doorbell. But I agree that if they are critical, voice assistant isn’t the way to go.
Hubitat push notifications and IFTTT notifications are solid. I’ve never missed a notification from either of those apps.
I may go back to that for the Chromecast. Is there a guide for TTS setup on that here? I’ve used it for sounds, but never speech.
To use the built in app, just install the Chromecast Integration (beta). Then use it to find your google/nest devices. It'll make all the HE devices per speaker for you.
If you have vlcthing setup to play sounds. Tts should just work via the speak command I think.
I posted working code in the vlcthing thread not that long ago.
Just getting coffee 
I have Chromecast (beta) installed. Currently just use it to issue stop casting commands, which don’t seem to work with Castweb API for some reason. I’ll try your methods with Castweb and if it doesn’t work out for me, I’ll circle back.
The final step will be to sell my minis and get two Echo dots to replace them. The Google home hub can stay. It has other redeeming qualities.
Yeah, lack of coffee. I forgot that the primary reason I setup Castweb API, was my preference for the official Google Assistant voice (the male voice actually, but close enough). I may have to settle with the built in voice though. Not a fan of the minis, so their days may be limited 
Hmmm, after some thought, (and coffee) another option that might work well for me personally is to use an old iPhone for Alexa TTS and connect it to the Google mini via Bluetooth. I wonder if that connection would be persistent? 
So I have the following devices:
I use the Samsung M3 as the main TTS speaker for all home announcements. This is absolutely rock solid thanks to @djgutheinz Samsung driver and app. The device is located in the kitchen above the upper cabinets.
I use the Sonos primarily for music BUT the front door Sonos is used for Welcome Home (@bptworld) greetings.
The Echo devices; using Echo Speaks (@tonesto7), are primarily for voice control throughout the house.
I utilize all Echo speakers, Samsung and Sonos Speakers for severe weather alerts from my NOAA app and also fire/security alarms.
The Google devices were/are to determine voice control in home. I didn’t like Alexa 100% and decided to try Google. Ultimately Alexa is the winner as Google STILL cannot do the many skills that Alexa can do and the issues that everyone seems to be experiencing. So these are slowly going to be removed from the home. Btw if anyone is in need of some devices I am willing to sell the Google Home and (2) minis if interested - just PM me.
So that is the state of what I use. I tried VLC with my tablets that are on the walls throughout the home but the volume absolutely sucks on these Amazon Fire devices. Hence the heavy investment in actually speakers.
I was having the same problem playing announcements on my Google Mini, but I setup a rule that executes the refresh command every 4 hours and that seems to have fixed it.
Yes, I think that helps. I loaded @bptworld 's app above and I see it doing it's thing in the logs.
@bptworld I came in from outside and closed our garage door but there was no announcement again. I am wondering if adding a Refresh a few seconds after the Initialize would help?
What do you think? thanks
Is your queue full again? Does the speaker respond when you try to speak from the device page? What was in the logs when it happened?
Lots of options here.