After stabilization sys-apps/iproute2-4.14.1-r1 there was a problem like a https://bugs.gentoo.org/show_bug.cgi?id=621662. After installation net-dialup/ppp-2.4.7-r4 this problem no more. Reproducible: Always
I'm sorry, but i was wrong. Upgrade on net-dialup/ppp-2.4.7-r4 does not solve the problem. I had downgrade sys-apps/iproute2-4.4.0 (>sys-apps/iproute2-4.14 in /etc/portage/package.mask) and then the problem disappeared. *** This bug has been marked as a duplicate of bug 621662 ***