We all have this moments when not only we didn't make any progress in that particular training session but we actually came out much weaker. But fortunately there's nothing to worry about.
Listen we don't live in an ideal world and there are many factors outside training that can mess up your results for a little while. It could be stress, lack of sleep, emotional overload to name a few. The key is to not be harsh on yourself, even if you don't feel 100% today, then just go lighter this time(anyway it's BETTER than nothing!)
So next time when you have this problematic day just smile and remind yourself "not now doesn't mean never"