This issue only impacts enterprise users using SSO.
Ad-Hoc Analytics currently doesn't support SSO.
Ad-Hoc Analytics is designed to time out after 20 minutes of inactivity by the user. In other words, if the user does not pull additional reports for 20 minutes, the session will time out.
For companies using the standard login, this is typically not a big deal, since Ad-Hoc Analytics simply re-authenticates using the standard credentials, and continue on. However, SSO users do not have that luxury, as Ad-Hoc Analytics piggybacks off of the Marketing Cloud login when SSO is used. Since SSO cookies tend to timeout quickly, this ends up requiring that your Ad-Hoc Analytics users reliance the product when they time out, as Ad-Hoc Analytics does not natively support SSO authentication.
To solve this issue, the design specifications of Ad-Hoc Analytics would need to be expanded to have it also support natively authenticating using SSO. Such an expansion is not considered a bug or product issue, but rather a lack of a feature.