I would second the SD card wearing out. I had a very similar problem on a Pi ZeroW recently.I think the slow Raspberry Pi goes into an I/O wait state and while waiting the CPU clock is reduced to save energy. It's possible the SD card on the slow Pi is slower or about to wear out. If running with USB boot, as you already noted there may be USB connectivity problems.
If SD card, I'd replace it. If USB, I'd try reseating the cables and maybe use the other socket.
dmesg showed the slowdowns were caused by I/O errors on the SD card. Since replacing the card (2 months ago) I've had no further issues.
Statistics: Posted by MarkDH102 — Tue Sep 10, 2024 6:06 am