a process having nice set is shown in the stat column with the value "R N".
the space in the middle breaks batch mode parsing with awk and other tools expecting whitespace as field delimiter.

the culprit is in https://git.busybox.net/busybox/tree/libbb/procps.c around line 475.

                        if (sp->vsz == 0 && sp->state[0] != 'Z')
                                sp->state[1] = 'W';
                        else    
                                sp->state[1] = ' ';
                        if (tasknice < 0)
                                sp->state[2] = '<';
                        else if (tasknice) /* > 0 */
                                sp->state[2] = 'N';
                        else
                                sp->state[2] = ' ';


apparently the code assumes a non-zombie process will never have nice set.