What causes intermittent crashing issues?

Doesn't matter the game, almost all crash about 30 minutes to an hour in. Occasionally doesn't crash for a day or two.

The console is just out of warranty, and has been factory reset. The console is in a well-ventilated area and is dust-free. All games have been tried on internal and external storage.

Reading through Microsoft forums has determined that quite a few people have had this issue, and the only fix is to send it back to Microsoft for $250 for a repair. However Microsoft won't state what causes this.

Anyone have suggestions or know what causes this defect in the console? Quite tech-savvy and have swapped Xbox HDDs with SSDs, complete factory OS flash, and a bit of micro-soldering experience.