Wrong stdout output for combination method (-w 4)

[Snoopy]

you have to specify attackmode combinator

-a 1

otherwise hashcat will turn auto to -a 0 and these attack only supports ONE input file, so your second file second.txt and your rule -k "u" is ignored

btw:
you can remove -w 4, this option is for workload and --stdout doesnt really produce "work"