When I use Minicom to capture data from a serial port, I need to save the big data into a file, named minicom.cap. However, if I press Ctrl+A and L to capture file,
minicom.cap
minicom needs a configuration file that is under root permissions and is stored at /etc/minicom/ and is named minirc.dfl.
Usually when you first run minicom for the first time, as sudo, you can save the minirc.dfl, as if you run as any other user it will not save.
That may be your problem.