Hi Cmn,
There is a feature flag to disable sandboxing of custom visuals. It is triggered by adding a query string to the end of your URL. Ex:
www.app.powerbi.com?sandboxVisualsEnabled=false
We are of course always hard at work to improve the experience for developers while also offering the highest level of security for end users. We are hard at work to resolve any reported issues and appreciate your assistance and patience.
Thanks,
Bashir