AXL 6 is buggy, that's a fact.
Be aware that when AXL returns a 401 unauthorized error, it doesnt necessarily mean your credentials are wrong - as evidenced by the fact that you can pass in one set of credentials, do a bunch of calls and when call manager feels like it, have some work and some return the 401.
Just an FYI from my own personal experience...
(e.g. I can start an app, have a call work, then the next call not work, returning a 401. Then without changing any code or my credentials, start the call process again and have it work. Note: This is NOT a throttling issue.)