For the moment I am still in the problem, it is really strange and long to fix.
For the rest, the migration went super good. All your datas are safe and even the builder even runs little bit faster.
In the coming hours I will put the builder in maintenance so better you come back tomorrow. Guess everything will be ok.
By the way, you still can download your creations and work anyways. Just the sandbox lacks.
Note: At the moment, when you force to pass with 'Retry' at 'uninstall', and then you stop at the install error, then your component IS now installed in sandbox.
It works I think.
They are only messages coming from I don't know wich (JFolder:
instance.