This seems to be a recent issue specifically with Chrome. I've had this same error for at least a week (maybe 2?) but only via the Chrome browser. I'm able to access Evernote Web via Edge and Firefox using the same URL, username & password.
If this was a device limit issue, the site (or app) would give the option to "unsync a device" (or upgrade). This specific error only provides the option to reload, which goes right back to the same error every time.
As a workaround (although I prefer web view in Chrome) I've installed the Evernote Windows app (https://evernote.com/download) and have been able to access notes there. Once the issue is resolved, I'll just "uncync" the Windows app and go back to my usual Chrome tab.