I am not certain if this applies to your case, but this is what worked for me with the following set up:
- Using Windows
- Add-in stored on the network drive
My problem was that after I installed an add-in it would show up (both IDE and as a custom ribbon), but after I closed Excel and reopened it the add-in would fail to load (no ribbon, no IDE).
- First step to fix this is to add a trusted location in Excel settings:
Trust Center -> Trusted Locations
You may need to select [Allow Trusted Locations on my network] before adding a location.
You can add just one folder, or, if it is appropriate, you can even add the whole network drive.
You may want to select [Subfolders in this location are also trusted]
- The second step was far from obvious to me. I also needed to add network folder as a trusted location in Internet Explorer of all things:
Settings -> Internet Options -> Security -> Intranet -> Sites -> Advanced
Then you need to add the folder path to the network folder that contains the add-in.
After completing both steps and reopening Excel add-ins in the network folder started to appear both in IDE and as a custom ribbon. These two steps were necessary part of installation for every user.
If you are using multiple add-ins you may want to consider using one network folder for them. You can also take a look at this question about network add-ins to see how they can be distributed in a more convenient fashion (one of the answers there is mine).