Most common reasons for studs to break are..
Cheap Chinese studs... I change out ALL to grade 8.8 About the same as US grade 5.
Incorrect mounting...mounts to both seat tube and down tube. Need as close to perfect fit.
I use RED locktite on all studs (if removal is desired heat is needed).
Proper torque 6mm 50-70 INCH pounds... 8mm 150-204 INCH pounds (I use 50 and 150)
I double nut with a nylock nut as the second one.
Here are some pictures of my mountings, I have never had a nut or stud, come loose, break or strip out.
I make these shims in order to get the proper torque. The nuts are too close to the clamp for a proper socket fit. I don't have a nylock nut on this illustration.
I make this "L" bracket to eliminate engine twist due to engine torque. This way I don't have to over tighten mount nuts.
Almost every bike frame needs a custom made front mount. The proper angle for the optimum mounting is 75 degrees.
.......A bought mount can be had