Hi,
According to the Mendix system parameters, 30 seconds sets as a timeout limit.
After 30sec, mendix general error pop-up is showed on the page. You should debug your microlfow step-by-step and find the node which cause the error. Maybe you can fix it quickly.
That default error is sometimes struggle in my project if I miss some backend validation. To prevent this control your logic as much as you can. Also, you should ruse error handlers effectively.