Auth: id_token_hint not sent to End Session Endpoint

We have a SWA where we can log in using AAD or a custom OpenID connect provider. In our case we are using an Identity Server 4 as the custom provider.
Everything has been working fine until some time last week where we started experience issues with signing out. We haven't been able to identify any changes on our end that would cause it.

After hitting `/.auth/logout`, we are redirected to the End Session Endpoint (https://identityserver4.readthedocs.io/en/latest/endpoints/endsession.html) of Identity Server:
`/connect/endsession?post_logout_redirect_uri=https%3A%2F%2F.com%2F.auth%2Flogout%2Fcomplete`.
The url is correct but according to the documentation a `id_token_hint` parameter should be passed as well in order to the `post_logout_redirect_uri` parameter to take affect. We kinda end up at the at a Identity Server page where `post_logout_redirect_uri` is lost and the user never gets to `/.auth/logout/complete`.

This is where it is puzzling us cause we don't know if the `id_token_hint` was sent in the past and suddenly isn't anymore? And is there a way we can configure it?