I'm having a similar issue, what did you do to fix it?
We have an environment set up with Okta as a single IDP and one (1) SP. We are able to log in on our SP and navigate the application. When we try to log out (we initiate SLO from SP), the SLO fires twice from the SP and the second SLO call fails, breaking the whole SLO. This will cause the current user to stay connected to Okta (The logout response status code indicates a failure but logout will continue).