I've also noticed that on multiple occasions. The only similar circumstances between the times I've experienced this is whenever I'm having trouble with my internet connection. No idea if that's the issue, but just mentioning it
Yup, this usually happens when javascript hasn't loaded. This can happen for a few reasons, for example, because of a slow connection, browser-addon (maybe like an ad-blocker), etc., or anything else that delays or prevents javascript from fully loading properly.