What you describe sounds more of a resource problem leading to slower response.
You did not tell us what software you are running, or whether you started with a fresh SD card on your second Pi, so I guess things to check:
- SD card wearout
- SD card corruption
- does the camera store images on the SD card and does not delete periodically, card nearly full?
- SD card contact problems
Heat may destroy hardware, but SD card is more vulnerable than the rest of the electronics in my experience.
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http://retro.hansotten.nl for retrocomputing with the 6502 cpu