Are you sure those are Lolin D32 Pros? Some of the off-brands are not capable of entering boot mode.
There are two buttons on those boards, one is reset and one is boot. After you click "go" (or whatever it says) to flash the board, click the boot button and release it. See if that gets it going.
I mean, reasonably sure. It is the 16MB LED model from this link from the documentation
The board itself looks like this (front and back), it only has the one button:
Holding the button while attempting to flash the board results in a "failure to initialize" error. Not messing with it allows it to complete the flash process as before but, again, nothing seems to happen afterwards.