Every time I try to run my app in the sandbox it fails and says the following message: "Couldn't deploy to your sandbox. Please, check the logs: Unable to deploy new model by Haydê Machado." And there's nothing about it in the logs. I have no idea about what could be causing this problem, someone had it before?
You can try to create a local deployment package, hit F7 within the mendix modeler, to find out if there are any errors creating the package.