It may also be affecting Linux Distros as well, see Webmin will not start on boot - Webmin - Virtualmin Community.
That system is supposed to run systemd, so it shouldn’t be affected in the same way.
FYI , been using the module in post 1 for years to manage zfs in webmin. Only issue is you have to use the old framed theme to get some of the functions to work. Which I don’t mind, I tend to use the lower overhead theme most of the time anyway.