why Hashcat v6.2.6 is slower than v4.1.0 (or 5.1.0)

[Noema]

Just a hunch, but maybe there is a bug such that it uses the optimized kernel in Versions 4.1.0 and 5.1.0 although it says pure kernel is selected.

You could figure out by feeding it long candidates and check whether you get any rejected candidates.

I have tried with your hunch, i created a file with some keywords, some length of keywords greater than 15 (because optimized kernal support maximum password length is 15)

Code:

ksdfsdf
asfa
1111111111223456
111111111223456
1111111111223456sdffwefo
sdkfsdf

Launch hashcat v4.1.0 without -O param, no rejected, here is the result

Code:

Recovered........: 0/1 (0.00%) Digests, 0/1 (0.00%) Salts
Progress.........: 6/6 (100.00%)
Rejected.........: 0/6 (0.00%)
Restore.Point....: 0/6 (0.00%)

Launch hashcat v4.1.0 with -O param, rejected 2 keywords

Code:

Recovered........: 0/1 (0.00%) Digests, 0/1 (0.00%) Salts
Progress.........: 6/6 (100.00%)
Rejected.........: 2/6 (33.33%)
Restore.Point....: 0/6 (0.00%)

So, it's other bug.