I use Squid on my Vultr VPS.
But recently, or at least to my understanding, Vultr switched from using wss:// with CONNECT or plain https:// for their “View Console” feature to wss:// with UPGRADE which is not supported yet by Squid, according to Amos Jeffries.
View Console is useful when you need to perform rescue operations or deploying new Vultr instances among other things. If you use Squid (like me), you have to disable it if you need the “View Console” to work. Else, you will get a “Server disconnected (code: 1006) error on the popup window.