What are you using to update? Obtainium? You're probably selecting a conflicting package to the one already installed. You need to select the correct one. I've made this mistake many times.
This happened to me the other day and then I realized that I had a duplicate of the app that was sandboxed on my phone. If you have a sandbox app like Shelter running it might be that, or simply check for duplicates of Voyager that you may not know about.
I think this was the problem. Downloaded it off the play store and tried to update it from Github. Totally forgot haha. I guess I'll wait until the update goes live on the play store