ceerker I don't know if it is the case, but suppose you go to https://indieclub.one
, click the login inside Flarum, get redirected to account.indieclub.one
for login, and then get redirected to https://www.indieclub.one
, this could cause an error like the one you have.
If you have setup canonical urls correctly (I suppose you have) it should always redirect to www so this wouldn't be possible.