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    Thanks for your response dda! Commented Nov 1, 2023 at 23:20
  • Why would a pin be labeled as a GPIO if in can't be properly used as a general purpose input or output? As in, shouldn't they just be labeled as just VSPI_HD etc instead to avoid confusion? Commented Nov 1, 2023 at 23:22
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    @Zach I don't think that's an issue, most of the pins on modern MCUs have multiple functions--you decide which ones to utilize. Checking the schematics, I don't see any external quad-SPI peripherals (as dda indicates, most commonly used for flash chips). Another indicator is that it's probably not the pins (aside from GPIO2, we've conclusively established that it's linked to a blue LED...but why is the LED bank dimly lightning up during initialization?) it worked with other ESP32-Wroom modules, which are also the modules used on the NodeMCU-32S board(s). Commented Nov 2, 2023 at 1:26
  • @Zach okay, I checked on the Espressif docs and yes, pin 16 is indeed not recommended to be used as a GPIO pin (it still can be, of course, but it could lead to unknown behavior as you've experienced)--nothing about pin 21 though. Commented Nov 2, 2023 at 16:56
  • @Zach it is possible to have different functionalities on the same pin - just don't use them all at once. In the case of the VSPI pins, if there's no Flash chip, and the VSPI bus isn't inited (eg if the code checked whether there's a chip, and didn't deinit afterwards, oops), they can be used. Commented Nov 3, 2023 at 8:16