Why does application output freeze on breakpoint in QtCreator?

Question

I've found that stopping a program in QtCreator at a breakpoint stops the program output. For example, the following program gives this output when it hits the breakpoint:

#include <QDebug>
#include <unistd.h>

int main(int argc, char *argv[])
{
    for (int i = 0; i < 20; ++i) {
        qDebug() << "Printing line " << i << "\n";
    }
    int a = 0; // <-breakpoint here
}

Output:

07:50:37: Debugging starts
2020-09-04 07:50:44.162658-0700 editor[3615:65377] Printing line  0
2020-09-04 07:50:44.162689-0700 editor[3615:65377] Printing line  1
2020-09-04 07:50:44.162695-0700 editor[3615:65377] Printing line  2
2020-09-04 07:50:44.162699-0700 editor[3615:65377] Printing line  3
2020-09-04 07:50:44.162702-0700 editor[3615:65377] Printing line  4
2020-09-04 07:50:44.162706-0700 editor[3615:65377] Printing line  5
2020-09-04 07:50:44.162709-0700 editor[3615:65377] Printing line  6
2020-09-04 07:50:44.162713-0700 editor[3615:65377] Printing line  7
2020-09-04 07:50:44.162716-0700 editor[3615:65377] Printing line  8
2020-09-04 07:50:44.162720-0700 editor[3615:65377] Printing line  9
2020-09-04 07:50:44.162724-0700 editor[3615:65377] Printing line  10
2020-09-04 07:50:44.162727-0700 editor[3615:65377] Printing line  11
2020-09-04 07:50:44.162731-0700 editor[3615:65377] Printing line  12
2020-09-04 07:50:44.162735-0700 editor[3615:65377] Printing line  13
2020-09-04 07:50:44.162751-0700 editor[3615:65377] Pri

It just stops mid string like this. I've tried redirecting output to the terminal, but that just exits right away, without outputting anything. If I add usleep(20000); above the print line, it will print out all (20) of the strings. If I add usleep(10000); it will get to number 16.

I'm using QtCreator 4.13.0, Qt 5.15.0. I'm using Clang that came with MacOS Catalina (x86 64bit in /usr/bin). I'm using LLDB that came with it (also in /usr/bin/lldb).

This is a fresh install of the OS, there is nothing else installed on the system except the programs that came with it. MacOS version is 10.15.5.