- Pi 2 had the camera flash reboot issue
- Pi 4 had improperly implemented USB-C charging circuit, causing many PD adapters to not power it[1]
(I still have and use both of the original models — the hardware flaw was only a problem in certain circumstances.)The Pi 5 has it's funky 5V / 5A requirement (though 5V / 3A works fine if you're not using high power USB accessories, if you have a decent power adapter), but it's otherwise not had any hardware-level odd quirk on the scale of Pi 2/4.
So the question is: what will it be on the Pi 6?
[1] https://hackaday.com/2019/07/16/exploring-the-raspberry-pi-4...