I think this is not a bug, but possibly an error configuration.
If you search for Loader under Admin -> System Configuration, are there any options changed here? If so, can you please change them to the original state?
If that doesn’t help, what browser are you using? And when you open the browser developer tools, what error messages are there here? Are there any hints in the OTOBO log?
What exactly does your installation look like? Are you using Docker and if not, how is proxy etc. configured?
I think if we answer these questions we can find the problem.