We had message aliases set up to forward voicemails to Google, and it stopped working a couple of weeks ago. We are currently running Allworx 48x
8.5.26.1. Any help would be appreciated.

Check your Googoo. I believe Googoo has been restricting "insecure" access to Gmail accounts that don't use MFA. I think you can still enable this but can't tell you from memory how to do that. This likely isn't an Allworx problem exactly. BTW, as I ought to tell everyone, that 48x is end of life and you'll not be able to update it past v8.5. Trade it in while you can for a current-generation server.
Once upon a time Allworx would proxy the E-mail without any configuration at all. I suspect (without evidence) that ended with the Windstream bankruptcy and all the hidden changes resulting from that.