First of all: I misread your initial question and fully glossed over your mentioning of the call activity and assumed you were referring to a task. A dumb mistake for sure considering the fact that regular tasks do support looping and Visual Paradigm fully supports the current formal standard to my knowledge.
When re-reading the BPMN specification then I don’t think this is an oversight at all. I think that using a loop within a call activity would actually violate the current standard.
Solely going by the specification: a loop applies to an activity. It is the activity itself that gets a looping behavior. Now mostly referring to tasks and sub processes.
But a call activity isn’t necessarily an activity. As its name implies it either calls a Global Task or a Process, and I think that the looping behavior should apply to those specific task elements, not the call activity itself.
I also noted that if you refer a call activity to a task which is looping then it will inherit the whole thing, including the looping symbol.
So quite frankly I don’t think there’s anything to fix here.
(edit): My opinion is also fueled by the definition of a call activity (see the specification): “The Cal Activity acts as a ‘wrapper’ for the invocation of a global Process or Global Task within the execution”.