Hi Roman,
This question might be more appropriate for the
jack-devel mailing list.
Jack devel <jack-devel(a)lists.jackaudio.org>
I agree with Patrick on that. You should report which distro and version
you are using, and also which CPU you have.
Is where a way to solve this problem?
Possibly building jack_capture from source on your own machine will help.
Cheers!
Daniel