I tried and failed to install SlicerRadiomics extension with the current Slicer preview. Is it expected? Sorry if I missed announcements and migration guidelines. I searched, but not sure where I should search - the error is not particularly helpful in informing about how the issue can be remedied.
Thanks for the report, it is a side effect of Upcoming downtime for download.slicer.org and extension manager due to package server transition - #3 by jcfr, issue has been identified earlier today and I am currently working on this.
For reference, this is now tracked in Installed extensions are not loaded · Issue #5786 · Slicer/Slicer · GitHub
To follow up, issue has been fixed by the following pull-requests (Slicer >= r30117):