Hi, I'm having the exactly same problem, it's not a connection issue, it's a browser issue.
That happens in Google Chrome and for what I look around seems that Google update Chrome and broke some parts of the Web Client, then Evernote team go back in time and revert the Web Client to an old version, because those bugs were already been solved in the past. I'm not from Evernote team and I deduced that for what I read. It's been a week this is happening.
I tried in Firefox and that happens too, the only Web Client that I found that still works fine is Safari.
An alternative is use the desktop client and apps, but if you change something in the note from the Web Client and save, the note will be broken again.
It would be interesting if the Evernote team could confirm or not what I said and give us a deadline for the fix, because this problem really leaves the product totally broken.
Long time user