Hi @the-lebowski,
I don't have experience with Okta specifically, but I wanted to ask you if you are using ISE or any other RADIUS server? How do you handle authorization part?
The reason for asking is that I wanted to sugest to go for secondary authentication option within AnyConnect - it is different server and another filed in AC login prompt to which different server can be defined. I had an experience with other MFA vendors that this was the only supported integration method, so I wanted to suggest to try that, if doable.
It looks to me that your RADIUS server doesn't support RADIUS Challenge/Response mechanism, which is required for interactive logins, where additional input is required from cliend. With push, it still requires MFA, but not via RADIUS packet, so your RADIUS server only returns Access-accept message back to ASA/FTD, which is why push is working for you (interactive part is happening in RADIUS backend).
Kind regards,
Milos