Does the saved profile show up in “unsupported” filaments (the sub-menu), or not at all?
The way Studio manages custom filament profiles, they’re always tied to a specific printer and nozzle size, and will not be selectable for any other nozzle size. For example the profiles saved from a project are always tied to the same printer and nozzle size of the project they were saved from, which sometimes trips people up. But those would typically still show up in “unsupported” sub-menu.
I’ve also seen Studio delete profiles at startup which it deems invalid (due to a syntax error or invalid value in one of the fields). Which is just rude. There could also be issues with cloud sync, if that’s enabled. One way to check all that is to view the local file system. Open the local configuration folder (eg. from Help menu), then inside the user folder there will be a default folder and probably a numbered folder if you log into Studio when using it. Inside either/both of those will be a filaments folder, and custom profiles are saved inside there. If they’re not being saved properly, or deleted at some point automatically, there’s some issue.
Also note that if you switch between being logged into Studio and not, the whole different custom profiles directory is used, so it may seem like custom profiles have disappeared. I suppose the same issue would occur if one uses different user accounts with Studio.
I did a deeper dive into presets in Bambu Studio presets management -- utilizing inheritance features
-Max