One more update, with apologies for the triple-post.
I received a secondhand original Pro1 in the mail from the indefatigable @Hook. Using the official flashing guide from this thread, I updated the Pro1 to firmware 20200825 and re-ran the initial setup process (including a one-time factory reset). The Pro1 was confirmed to be working normally. However, when I unplugged the original Pro1 screen frame and plugged in my Pro1 X screen frame (with the replacement Elephone screen attached), the Pro1 immediately entered a boot loop.
I then went back to the guide and reflashed all the firmw