Axios hijacks the back button. The TLDR is: we’re building too much speculative capacity and the “if we build it, they will come” assumption will be proven wrong.
It's always a bug. Usually, some issue with an iframe navigating to another html page, which makes the back button go back in the iframe instead of the page itself. This usually happens because of an ad, which makes me wonder why people are still navigating without ad blockers.