Oh that is actually very interesting. I haven’t seen the 20-second-led-on behavior before. If I had to guess, I would guess there’s some strange interaction happening with the SD card when you connect to the meter. There have been a couple of users reporting oddities with certain brands of SD card. But if it’s not interfering with your ability to use the meter, I wouldn’t worry about it for now.
Thank you for the details! Let me know how else I can help.