Not sure what happened there.  It's not entirely improbable that you would mine 3 or 4 blocks in a row.  What I believe would be a somewhat likely explanation: you found a block that was not the best solution (this happens frequently with alternate chains on any blockchain), but was still valid. It follows that there would be a succession of blocks thereafter that were correct solutions but not optimal ones.  When that occurs, the other miners can be mining on a separate chain from you, until the nodes reach a consensus as to the best proof submitted for work completed (blocks solved). The longer chain prevails, and multiple chains can exist simultaneously before one chain shows itself to be longer, and the network agrees.

This is the exact reason that I increased the # of blocks before a mined reward can be spent.  If it were lower than 25... there would be issues.  I've been contemplating raising it even further as a buffer. Hope that all helps.