Can you please try upgrading to the build out on download center Version 1.1.6582.41691 (Build 14.0.600.442), Released: January 10, 2018. We think the fix for cascading parameter bug actually made it into that build. In the changelog there was a bug fix mentioned as Model.GetParameters returning 400 which we think will cover the cascading parameter issue as well.
With the March 2018 release of Power BI Report Server the subscription cascading parameter issue has been resolved.
Unfortunately it appears that this release has introduced a new bug now with all of our Report Headers and Footers and making references to Parameters! in expressions we are getting #Error on expression logic. I will add a new item to Forums for this issue, but this one for sure is a show stopper.