We have this issue a lot with our users being partly field and partially office working. If they're here at the office (or any of our offices) then they have to join the domain when connecting to the network, and while they're out at a jobsite running off of a hotspot they'll have to enter in their credentials. For the most part, not many of our users complain about this, as it is a minor inconvenience. I personally will tell them to just type in their credentials when this occurs as there isn't a way yet to automatically sign them in if they're not joined to the domain.
We started having this same issue a few weeks ago. Users are promted for login by IWA as well as Okta. Something changed in the past few weeks because this wasn't previously an issue. Any help would be appreciated. We still have an open case, but Okta support has not yet been helpful.