Hello John,
Please be informed that there is an indirection between FreeCAD and Open CASCADE Technology developers, as FreeCAD project is done by another community and OCCT framework developers do not recieve bugs directly from FreeCAD users. A couple of years ago, a few FreeCAD activists started translating some FreeCAD bugs to OCCT Bugtracker, which is a good sign, as registering issues to C++ framework is not the same as reporting bugs to GUI application and requires additional efforts to reproduce and confirm issue.
As an open source project, OCCT gives community possibility of fixing bugs and extending functionality, but so far, the main development is driven by Open Cascade developers, which in turn depends on requests and feedback from commercial projects and customers.
OCCT 7.5.0 release includes 3 bug-fixes directly related to Fillets functionality (+1 related to Visual Studio 2019 compiler bug also affecting Fillets). This, indeed, doesn't look optimistic comparing to about 25 bugs on Fillet and Chamfer functionality reported by Community on bugtracker (the amount of bugs might look larger than it actually is, as different use cases might result from the same bug in the algorithm).
External contributions could be helpful in solving algorithm bugs and limitations.