bg command not sending process to background

After pausing the process with Ctrl+Z, I attempted to send it to background with the bg command.  Unfortunately, the process isn't sent to the background, and reappear to be running foreground.  Then, I do a Ctrl+Z again in order to pause it again.  Unfortunately, the key combination is no longer responding, and the process is still ongoing.  To make matters worse, the command is a for loop on many items.  If I hit Ctrl+C, the job will resume on the next iteration, and until the last iteration. Running on tmux inside iTerm on macOS.