Backand.signup() - "Create My App User" failed to perform

I'm trying to register a new user using:

Backand.signup(firstName, lastName, username, password, password2);

but I end up getting:

POST https://api.backand.com/1/user/signup 504 (GATEWAY_TIMEOUT)

When I check the logs (Log > Server Side Exceptions), I notice this error:

An unexpected signup exception occured The following action: 
"Create My App User" failed to perform: The operation has timed out 
The operation has timed out Exception has been thrown by the target 
of an invocation. The operation has timed out

I haven't touched the "Create My App User" script.

Security & Auth > Configuration > Public App: Turned on and set to User. I've also toggled anonymous on and off and switched between ReadOnly and User in case of a permission issue.

It was working just fine a few weeks ago, and a few times I was able to get an entry into the Security & Auth > Registered User's table, but I can't get it to create any new entries in my app's user table or even work at all now.

Any help would be appreciated.