RPCMOUNTDOPTS="--manage-gids -U" prevents to start nfs-kernel-server

[AnOctet]

A UDP is disabled in order to provide only TCP transport. In /etc/default/nfs-kernel-server following options set for rpc.mountd (http://manpages.ubuntu.com/manpages/bionic/man8/mountd.8.html):

RPCMOUNTDOPTS="--manage-gids -U"

No other changes are applied. Further,

~# service nfs-kernel-server restart
A dependency job for nfs-server.service failed. See 'journalctl -xe' for details.

Output of 'journalctl -xe':

Dec 25 19:06:09 debian systemd[1]: Failed to start NFS Mount Daemon.
-- Subject: Unit nfs-mountd.service has failed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- Unit nfs-mountd.service has failed.
--
-- The result is failed.
Dec 25 19:06:09 debian systemd[1]: Dependency failed for NFS server and services.
-- Subject: Unit nfs-server.service has failed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- Unit nfs-server.service has failed.
--
-- The result is dependency.
Dec 25 19:06:09 debian systemd[1]: Dependency failed for NFSv4 ID-name mapping service.
-- Subject: Unit nfs-idmapd.service has failed
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- Unit nfs-idmapd.service has failed.
--
-- The result is dependency.
Dec 25 19:06:09 debian systemd[1]: nfs-idmapd.service: Job nfs-idmapd.service/start failed with result 'dependency'.
Dec 25 19:06:09 debian systemd[1]: nfs-server.service: Job nfs-server.service/start failed with result 'dependency'.
Dec 25 19:06:09 debian systemd[1]: nfs-mountd.service: Unit entered failed state.
Dec 25 19:06:09 debian systemd[1]: nfs-mountd.service: Failed with result 'exit-code'.
Dec 25 19:06:09 debian systemd[1]: nfs-idmapd.service: Unit is bound to inactive unit nfs-server.service. Stopping, too.
Dec 25 19:06:09 debian systemd[1]: Stopping NFSv4 ID-name mapping service...
-- Subject: Unit nfs-idmapd.service has begun shutting down
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- Unit nfs-idmapd.service has begun shutting down.
Dec 25 19:06:09 debian systemd[1]: Stopped NFSv4 ID-name mapping service.
-- Subject: Unit nfs-idmapd.service has finished shutting down
-- Defined-By: systemd
-- Support: https://www.debian.org/support
--
-- Unit nfs-idmapd.service has finished shutting down.
lines 1396-1436/1436 (END)

Everything working fine if '-U' option replace with '--no-udp':

~# ps aux | grep rpc.mountd
root 3516 0.0 0.0 37704 704 ? Ss 19:10 0:00 /usr/sbin/rpc.mountd --manage-gids --no-udp
root 3534 0.0 0.0 12784 968 pts/0 S+ 19:10 0:00 grep rpc.mountd