@devrom  Well, the most likely culprit would be QBO's severe allergy to cookies.

Even on something as straightforward as this support community, after being logged in for a week or two, it'll start getting very fussy; I normally have to wipe my QuickBooks cookies every two weeks just to be able to log back in and post here. It'll act like you're logged in, but you won't actually be able to do anything.

Try logging on in an incognito browser with the problem users; if it works, there's your sign.