Walther PPS light primer strike?

[LAFLA]

At the range yesterday my wife had a light primer strike and FTF with her PPS 9mm. You could see a slight indentation on the primer. Her EDC is a Kahr PM9 but she is leaning more and more toward switching it for the PPS on a daily basis so she was a bit concerned about the failure. She has about 400 rounds through it, mostly 115 gr WWB and until now, not a single problem. She was shooting one handed from her weak side and when she reloaded the cartridge, it fired just fine. She asked me if limp wristing or other bad technique could have caused. I told her honestly that I didn't know. Any thoughts on this? If it was just a bad round, that would be ok since she carries Speer Gold Dots or Federal HST on a regular basis and hasn't had any problem It's interesting as between the two of us, we have fired probably 8000 rounds of WWB with no previous issues.