I am very surprised by the validation function in Bizagi modeler.
I did a simple test, and created an imperfect flow, (see attached File "error.png" ) but the only error I got was for the start event not being connected.
The validation doesn't complain about missing outgoing sequence flows from the tasks or the missing end event.
When I connected the start event with the task, I got no error. (see attached file "noerror.png").
If I create a similar flow in Visio, I get a lot more errors, as I should I think. (see attached file "visio error.png").
Why does this happen? Does the free version not validate against all applicable rules for the shapes used?