I happened to find a huge difference in QRDecomposition between 12.0 and 12.3. The QR decomposition of the sparse array in the following notebook file finishes less than a second on 12.0.
However, it gives a warning on 12.3: N: internal precision limit MaxExtraPrecision=50.` reached while evaluating. Showing the stack track tells that the Mathematica is getting the Sign of this number, which is actually 0 after simplification. Is there any way to get rid of this internal numerical simplification?
I wish someone can fix this issue in future release.