After loading a set of pics, both automatic preview via Align button on assistant tab or using Images->Create Control Points + Optimizer->Optimize Now! + Fast preview button very likely (but not 100%, more like 90%) busyloop the preview window.
However, when creating control points manually, but before hitting Fast Preview button, save the project, exit Hugin, re-load project and after that Fast Preview works most of the time (again, not 100%).
If this helps...
After loading a set of pics, both automatic preview via Align button on assistant tab or using Images->Create Control Points + Optimizer->Optimize Now! + Fast preview button very likely (but not 100%, more like 90%) busyloop the preview window.
However, when creating control points manually, but before hitting Fast Preview button, save the project, exit Hugin, re-load project and after that Fast Preview works most of the time (again, not 100%).