Issues during BRepAlgoAPI_BuilderAlgo::Build and SimplifyResult

I am getting the following warnings during BRepAlgoAPI_BuilderAlgo::Build:
1. BOPAlgo_AlertBadPositioning
2. BOPAlgo_AlertNotSplittableEdge

What are the possible reasons for the above?

Additionally, the SimplifyResult step isn't merging all the faces together. What could be the problem there?

Below is my code:

BRepAlgoAPI_BuilderAlgo builder;
builder.SetArguments(listOfSolids);
builder.SetRunParallel(true);
builder.SetGlue(BOPAlgo_GlueShift);
builder.Build();
builder.SimplifyResult();

I confirmed that the SetGlue step isn't causing the problem. The solids have no overlap.