Hello Andrey, Thanks for finding this issue with cryptmount, and for your helpful stack traces and configuration information.
I am still investigating this issue, and have created a new test specifically for LUKS partitions within ordinary files to help narrow-down the source of the problem. Could you confirm that in your case, the LUKS container is in an ordinary file on a local filesystem (e.g. there are no NFS/SSHFS/NTFS filesystems involved)? I've confirmed that cryptmount does handle these files as intended on debian-jessie, debian-stretch, ubuntu-artful, but there do seem to be issues with debian-buster and fedora-27. All functionality relating to handling LUKS containers within ordinary block devices (e.g. hard-disk partitions), or filesystems in ordinary files managed by other cryptmount keymanagers (e.g. "builtin", "libgcrypt") seems to be working as it should. I hope to be able to provide a fix soon. RW Penney
