Hello,
I'm not sure if you know about it, but Sparse 1.4 is available here. It contains a reasonably large suite of test matrices. When built, the 'bin/sparse' program will generate solution vectors that are fairly easy to compare with the output of SpiceSharp's Sparse implementation.

I have been trying a handful of these matrices. While many have been uneventful, I have found one - sptrMondo.tr.mat.gz - that seems to be a problem. To be fair, it is a very large matrix (20757x20757, with a total of 279967 elements), and takes Sparse 1.4 a while to solve (~23 seconds on my PC). But it was so slow that I gave up waiting for the C# implementation to finish. At present, I can't be certain whether it is very slow to solve or getting stuck in an infinite loop.

I should also mention the SuiteSparse Matrix Collection, here, which contains more test matrices than any reasonable person could ever conceivably desire!