BTS labor tickets - Error 547

Legacy Contributor

One of my customers is getting the Error 547 - Insert conflicted with Foreign Key FKEY0048, I checked the indirect codes and they are ok and the default indirect id is set. This error seems to happen in a random way, it occurs frecuently but not always. Doing some tests I could reproduce it only once and after that I couldn´t reproduce it anymore. However my client is still getting this error.
Any idea of what else can it be?