Let's diagnose the failure before we start trying to fix it.
When you say the rounds "fail", what do you mean? Do you mean they fail to chamber? Fail to fire? Fail to extract? If your problem is that the slide will not close fully on them then take a couple of filing rounds, color them with a Sharpie and try chambering them again. When you eject them, note where the Sharpie has been worn off the case. The is the first place to look for a solution.
I'm going to assume the result and continue. If the problem is at the case mouth then you probably just aren't removing the belling of the case mouth adequately when you seat the bullet. Adjust the seater die down a little bit at the same time you're adjusting the seater stem up (so that you don't seat the bullet any deeper). This will increase the crimp applied by the seater die. Retry the Sharpie test and adjust the crimp as needed to fully remove the belling at the case mouth. If this is the problem, you will eventually find the sweet spot.
I started loading 9mmm with a Lee die set. The powder through expander and I did not get along. Either I couldn't get enough expansion and the bullet would collapse the occasional case mouth or the mouth looked like a Pilgrim's blunderbus. I have Lee dies. I use Lee dies. But I retired my set of 9mm Lee dies and got an RCBS 9mm die set and all of my problems went away overnight.
If the Sharpie shows the case is binding near the case head, then the brass may be a little large. The conventional resizer die cannot get at the part of the case that is surrounded by the shell holder and so a little bit near the head escapes being resized. The Lee FCD die is designed to solve this problem.
I don't use a Lee FCD because I am opposed to the very idea of performing a "post-sizing" operation on a cartridge and so I use a micrometer on each case as it enters my reloading stream and if the diameter near the case head is too big, it is simply recycled. By intercepting outsized brass before it enters the reloading stream, I save myself the time and trouble of running everything through year another die, but if what I do seems like a lot of work to you, then by all means make the investment in the FCD. You won't be disappointed.
If the Sharpie mark was somewhere else, PM me and I'll be happy to work with you to diagnose the problem.