A week ago, I encountered the same problem like this. Sometime I can login and can't login. When I view Activity Log, here is the log:
18:24:33 [ERROR ] [2820] [2256] 0% HTTP request failed, code: 429, error: OK
18:24:43 [ERROR ] [2820] [2220] 0% HTTP request failed, code: 429, error: OK
18:24:45 [ERROR ] [2820] [3196] 0% HTTP request failed, code: 429, error: OK
18:24:55 [ERROR ] [2820] [2284] 0% HTTP request failed, code: 429, error: OK
I tried the Evernote Web version but it can't login too, it alway send 418 HTTP Status Code with a blank page. To post on this thread, I must use VPN.