FreeCAD 100% here. I find the sketcher solver mostly works fine, but it helps if you can give the solver unambiguous constraints. It's often easy to give constraints that happen to have to 2 symmetrically opposite valid solutions. Have you seen these tips on giving Sketcher constraints that make the solver's job easier? https://wiki.freecad.org/Basic_Sketcher_Tutorial#Additional_information
FreeCAD also encourages a workflow using multiple simple sketches rather than a few complicated sketches, which would also make the solver's job easier.