I found that if you resize the first monitor window, it starts working. I've also gotten the "first never works" effect when launching the separate monitor window, whereas second and subsequent windows always work fine. So for some reason, resizing it allows it to move on from the hollow cursor and start printing the prompt and so forth. I never tried to blindly type into it.
clang thinks some || perhaps should be | instead in the source.
mixup (pun intended) in INSTALL doc
malloc.h missing on macos, deprecated on other BSDs too.