I have the same issue that Silarous described. The only difference is that I am using a PI4 2GB instead of a Pi4 4GB.
I noticed that the fan (HW/SW) does not allow my board to boot. It gets stock somewhere. The only way to allow the board to boot is to remove the fan :-/.
I compare the pins used by the fan 5, 8, 10, 11 (Button), 12 https://pinout.xyz/pinout/fan_shim#
vs the pins used by the LCD https://www.waveshare.com/3.5inch-RPi-LCD-A.htm
As you can see the pin that seams to bee the issue is pin 11 (TP_IRQ).
I don’t need the button on the fan. Is there any way to completely disabled this circuit to prevent any interference with the LCD