I have a problem with a List ribbon button that disappears. The only thing that has happend that I know of is that the wsp was redeployed and the site-feature (which creates the list) was reactivated. But somehow, the button won't show anymore... Anyone who has an idea what the problem could be here?
The anwser to this problem is really strange... I forgot to mention I've edited the page in my list and changed the "Toolbar type" in the list-view-webpart to "No toolbar". But by setting this, custom action buttons in the ribbon hide...
So I solved it by setting it to "Full toolbar" again, and the ribbon button becomes visible again!
There would be a few things for you to check, but it goes down to simply investigating what the solution package is doing (provided you are using the rest as being the Out-of-the-box styles and master page from SharePoint).
Try deactivating whatever Features is activating. If any custom Action is part of the feature, or a faulty CSS class is doing that, at least you should be able to notice it.