I expect that OH 3.3 comes with Californium 2.0, whereas 3.4 milestone build has switched to 2.7
I added the jar build to the Community Market Place, The binding does not yet show up, you need to enable the market place and previews (both options in Settings:Community Marketplace)
- remove the files from the addons folder
- Go to Settings:Bindings and search for “Shelly Beta with Plus/Pro support”
- install the binding