Uboot-envtools.sh not producing fw_env.config

Turris Omnia - rtrom01
Turris OS 3.9.6
Kernel 4.4.119-082ea0f4a4e204b99821bedcb349ed54-0

After having added the x-bit to /lib/uboot-envtools.sh and executed the script as root from cli it was expected to find etc/fw_env.config but it seems that file is not being produced.