It's difficult to provide a useful response with such limited information.
Stay objective. The first step would be to look at where the hard fault happens. Use a hard fault monitor to understand why it is happening.
Avoid the temptation to think that if an error doesn't occur, then the program is correct. Or to somehow believe that because it sometimes runs, the problem must be with something other than the code. If something isn't working, the most common culprit is the code. The second most common is the hardware (bad power supply, bad schematic design, improper assembly/soldering, etc.). Everything else is much less likely.
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