Yes I vaguely recall having that experience with ceni as well because ceni worked when connman wouldn't for me on a couple machines. There is a way to get ceni to retain (search upstream). In the end, I got connman happy but it took some reading at the antiX forum.
My guess is that we all try everything to get something to work and it's quirky when one is new to antiX...and/or some people need to blacklist things, etc. Blanking at the moment, but you may have to start with a vanilla /etc/network/interfaces (or at least inspect it vs a vanilla one).
Re Network Assistant, John added that for a corner case user that I can't recall, but it makes it easier to disable/blacklist and worked better for someone. antiX net tools are more of a toolkit evolving to support a wider set of users.
Sorry been away while forum was undergoing maint so don't know if you are still around / still having issues (or if you've sucessfully connected as static).
If you still have issues, let us know (and please post an inxi -Fv7). Make sure you've done the DSL File Restore, then update && upgrade. That'll get you all the firmware + man pages + other stuff that couldn't be fitted inside a CD plus get everyhing up to date.
Perhaps not necessarily for you, but newcomers to DSL (antiX23-based) may benefit from the sort of "getting started" post
upstream which covers some of the quirks.
@John - Maybe that belongs as a sticky?