Hey there, thanks for playing! I'm glad you like the game.
Sorry about those issues, the coins disappearing is definitely a bug! I will try to upload a fix for that and the Bat quickly.
Thanks for the suggestion. Didn't realize it would be small on a surface pro, so thanks for the heads up. The extrude tool is also a good suggestion, will hopefully include it in the next update.
This sounds like a pretty serious issue. Would you be able to email me at firstname.lastname@example.org with screenshots of the exported model, as well as screenshots of what it looks like in-editor. Additionally attaching the exported obj and mtl files would be helpful.
I will try and fix it as soon as possible.