Singularity warning is an analysis stop warning of occurred mathematical nonconformity, which will help you to save time because an unrecommended model setup has been defined and the analysis might take a lot of time without giving any reliable result.
Description of singularities (nonconformities) can be found in the Results and Analysis tab. Also, the model fault can be usually seen in the 3D presentation.
In the video, the singularity issue is explained as well as the consequences of their appearance and how to fix it. Several examples where singularity can appear are shown.