A few things can go wrong with Lacto fermentation if you use the wrong equipment. The key is to create an air tight environment. This is because air helps bad bacteria and yeast thrive. I messed up my first batch by using a lid that didn't seal and air got into the jar which allowed yeast to grow on my pickles. Also it is important that you let out the natural pressure created from the fermentation process so your jar doesn't explode. The only way I found to do this was to use an airlock lid called a "kraut kap". I think you can get them from amazon. This lid is specially designed to let pressure out without letting air in.
Good luck! I hope the next batch comes out great!