Noclip not working sometimes
So I know the functions of the typical server commands before someone suggests them to me; server.writecfg, ownerid, noclip/debug.noclip, etc. We've used all of these in several orders, we've removed all plugins, we've reinstalled the dedi server (HostHavoc). We've tried removing the owners and readding, rejoining, then restarting the server- all in several different orders to try to fix it. It seems to work SOMETIMES but the server eventually reverts back into us not being able to use NoClip.

Although we're allowed to spawn items, use other commands, etc, once we're set as owners. We have found no way to actually fix this but it severely hampers our ability to swiftly check out the server, and for the future of admin-ing it.

As far as I'm aware, noclip is a Rust client-side command, nothing to do with Oxide. You have said you removed all plugins (and presumably any data/config files associated with them) before then doing a clean server install so I'm at a loss to why you have this problem. Maybe talk to your hosting provider or see if anything pops up on FacePunch bug reports.
antihack.admincheat true?