Having trouble with "NetworkError" message

[xfbs]

Hey guys,

First of all, Wiki.js is awesome. Thanks for the work on it!

So we are encountering a strange error using it. It works fine normally, but when you edit a page, it'll spin for a couple seconds and then say "NetworkError". Looks like this:

After that, it'll say in the page that there is a conflict:

However, when you close editing the page, selecting "Discard changes", the changes are actually there. So like, saving actually does work. It's just that for some reason it sais that it doesn't work.

In the logs there is a single request happening that does not have any result, it seems:

And then, in the server logs (we are using an NGINX reverse proxy) we can see what looks to me like TWO request, both erroring out with a 499 response.

What's up with that? Did we configure something wrong? Please let me know, any help is appreciated.