Yes, I have noticed that many of the "reference solutions" for my own problems seem to have been lost (they still appear when I edit the problem, they just disappeared from the list of scored solutions) -this explains the generalized drop in scores seen some time back. No idea what might have caused this, though. Some times a solution is "lost" if, during rescoring, it times out or runs into a general cody-level error (the same behavior when you create a solution that times out, which is not recorded as a failed solution at all). This might be intentional to avoid keeping solutions that may cause timeouts from being rescored, but it can have undesired consequences so it might be desirable to fix this behavior to avoid this sort of "lost solution" situations... (although I am not sure if this is related to this particular case of lost solutions). Thoughts?

Recommended https://blogs.mathworks.com/cleve/2012/11/12/magic-squares-part-3-linear-algebra/

Jean-Marie, I believe that maybe these reference solutions were erased simply to save some unnecessary occupied space since they are not required. It's best to store your solutions at Github or your own pc.