Stuck on 'Loading Data'

I have one laptop which cannot login to home assistant.

I can login on my mobile app, mobile browser, desktop PC and another laptop, but I have one machine that will NOT load the lovelace UI, after logging in it just sits there ‘Loading Data’ before eventually timing out to the ‘Unable to connect to Home Assistant.’ page.

Previously the UI was working on this machine, went to refresh the page and this problem started.

I’ve cleared the complete browser history, cookies data, restarted HA, everything I can think of, but it makes no difference.

What’s going on ?