Hi, my girlfriend had this problem and I wanted to let you know what it was and how I solved it.
The issue is that dominion.games' SSL certificate is uses USERTrust RSA Certification Authority as a root certificate authority, and USERTrust is not trusted as a root certificate by old versions of Mac OS. Might also be a problem in Ubuntu. It's not a browser problem and clearing the cache or even switching browsers won't help.
If you're a Mac user and you're encountering this problem, updating to a newer version of macOS (Sierra or later) should solve the issue.
You can also fix the issue on a Mac without updating. Here's what I did:
- Open dominion.games in Safari (even if you usually use another browser)
- Click "show certificate"
- Click USERTrust RSA Certification Authority
- Click Trust and change it to "Always Trust"
- Enter your password to confirm
- If you normally use a browser other than Safari, close that browser and re-open it so it picks up the new change.
This should solve the problem.