I have an XDM 5.25 in 9mm. It has no less then 10000 rounds handloads thru it. Last year is developed a hair line crack in the breech face. Springfield installed a new slide no problem but another crack is developing in the same place.
I do not load hot rounds. If the load data calls for 4.4gr to 4.8gr I load 4.6gr. I shoot jacketed or plated bullets only.
Since the first crack developed I've been checking the breech face after every outing. I noticed this recent crack after shooting 12 rounds  with 100 grain bullets over less than maximum charges along with my regular 124gr. loads.
I'm going to return the gun to S/A for repair but I need to know if I am doing something wrong or is this due to design or materials.
I like the XDM 5.25 a lot and want to keep using it. I even bought a 2nd XDM 5.25 but in .45 auto.

Any ideas on this issue?

Thanks for your time
VonBark
EDIT to say the current slide has no more than 1500 rounds on it.

Is SA pushing things or bad QA?

Correctly hardening slides has been difficult forever.

Less important in a low pressure design for .45 ACP but still not error free.

The mass of the rear of the slide and the non-uniform sections in the slide have a long history of being an issue in heat treat.

Are they inadvertently leaving parts hard enough to be brittle with interior stress remaining?