Hi, thank you.
yes it looks like SSL certificate issue, but SSL checker(
https://www.sslshopper.com/ssl-checker.html ) shows that certificate is correct.
I've never clicked 'proceed anyway', because main server in production at least 2 years, and certificate is valid.
I see the same problem with new PC, where this site was never opened and into incognito mode.
When first URL was opened and WSS connection established for example to wss://web.serverid.server_url/web-connect I still have the same problem with another servers, for example
wss://web.serverid1.server_url/web-connect
wss://web.serverid2.server_url/web-connect
and so on. After opening such URLs into browser application can establish connect, until next time when it received new URLs.
And it works in Firefox.