Writer hangs while opening signed .odt files in Ubuntu 16.04.3

When I open a signed .odt document the app hangs, like this:
LO Writer hang

libreoffice <filename>.odt

produces no stdout: no error messages, nothing…

Tried signing with OpenPGP and X.509 certificate - same result.

**From Writer**
Build ID: 1:5.4.0~rc3-0ubuntu0.16.04.1~lo1
CPU threads: 4; OS: Linux 4.10; UI render: default; VCL: gtk2;
Locale: sl-SI (en_US.UTF-8);
Calc: group
GPU: nVidia 450 GTS
Driver: xserver-xorg-video-nouveau-hwe-16.04 (1:1.0.14-0ubuntu1~16.04.1)

Disabling MUFFIN solved this problem