Cool… I’m also developing custom activities for Uiapath. So would be able to work with you get it sorted. However I haven’t seen this issue that you are facing. But I have few scenarios that we can check on…
First the .net framework.
In your visual studio solution check the framework you are using. You can do this by opening the solution and right clicking on the main solution item and getting on to its properties. There it has a option to change and see the framework version.
.net framework in UiPath studio. Open the studio and go to help page. There just below your device I’d and rest of the info, you can see the .net framework version its using. Make sure Uipath studio is using the same or higher version.
Next the custom activity version.
I don’t know how this happens but it happened to me couple of times.
Say in version 1.1.0 nuget file you had only one activity. Next you do some updates to your code and add a new activity. Say you updates the dll file of the 1.1.0 nuget file without changing its version. Now you delete the dependency in Studio and add it again. If this happens, you will only see the 1st activity that you had. And the newly added will not be visible even though you updated it with the latest dll file. However if you change the version of the same nuget file to 1.1.2 and add it as the dependency it will have both activities…
Try that out and see how it goes…