I just downloaded the most recent version of this plugin, but it doesn't show up in my DAW, even though I rescanned it multiple times
I'm not sure what 1.0.3.1 refers to, but GuyEngine V2 is currently on version 1.2.3. When updating to a new version, make sure you either completely replace the previous version, or delete it entirely. Older versions can cause conflicts with newer versions.
Also make double sure that everything is in the correct folder. Additionally, if you're using VST2 and VST3, they must both be updated or they can conflict and just not work.