yeah, the important thing is to figure out WHY the screws are shearing. Stuff like that isn't high quality from a fastener standpoint. There could be flaws from forming the thread, or they could be going not an unseen piece of metal and over tightened.
But properly designed, a joint should always load the fasteners in shear and they should not fail, so this indicates bad parts, a bad design, or both.
If you have access, the good news is they should not be hard to remove. I'd think a left hand drill bit of about 50% of the remaining diameter should do it. You'll need a really hard bit - cobalt, and it will be difficult to start, but the remaining part of the fastener shouldn't have a lot of torque left on it.
Post a high magnification picture of the end of the bolts - the shape of the fracture surface tells a lot.
Then you have to figure out how to take load off the joint, or it will just keep happening, unless the parts were simply over tightened into a piece of metal.
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