I've been having the same issue as reported
here for a few days now. I've made NO changes to my config or login credentials, and the same credentials work fine to log into my.jdownloader.org from my web browser. I've logged out and back in multiple times to be sure.
I run JDownloader2 headless. I connect to the server with SSH, so you can rule out telnet copy & paste issues. I checked my org.jdownloader.api.myjdownloader.MyJDownloaderSettings.json and the credentials are correct there. They match my password manager, and I can copy them straight from the json into the browser and they work there. So I don't see how it can be any kind of hidden character/encoding problem. Plus, as I said, I hadn't touched the credentials in any way and they'd been working fine up to this point.
When it prompts me to reenter them I've tried typing them in manually, just in case. Makes no difference. I've reentered them about ten times in a row just in case jd2 had multiple threads each trying to get the correct credentials, never helped.
I tried renaming my /config directory and starting completely fresh, entering the credentials manually when prompted, they still don't work. I can't think what else to try.
It really doesn't seem like the credentials themselves are the problem. It's very possible there's some other connectivity-related problem and your exception handling is just mis-identifying it as a credentials issue. But there's so much logging I just don't know where to look.