If with "JFK", you mean the FSDT JFK, that surely cannot be, since we surely have Pushback at all positions, unless you have another AFCAD in conflict with it.
If, instead, with "JFK", you mean the default JFK or another 3rd party JFK scenery, then it's possible there's a problem with its AFCAD, likely all Pushbacks defined as "None", which you can of course override, using the GSX parking customization page.
The same page, will also tell you which AFCAD is being used by GSX, which will be helpful to find conflicts.