We want to thank David, AD4WX for taking time to let us know the correction for this issue.
In short, when doing a Repeater Book (or RFinder) search, the app will lock up with a force quit required.
The problem has surface with MacOS Big Sur 11.2 and seems to be tied to the tabs functionality in apps. The correction is as follows:
In System Preferences, General there is an option to set the Prefer tabs function to always, never or in full screen. Setting this option to Never or in full screen keeps the problem from happening. Always is the culprit.
May 18, 2021... Always believe you can.