By Bradley Grafelman 1242018
#515292 Which aircraft(s) have you tried?

The "problem" is perhaps that the addon aircraft is using custom FSUIPC offsets to reflect the transponder state. There's nothing vPilot can do to "fix" that; the common workaround is to use a LUA script with FSUIPC to replicate such data to the SimConnect data area that vPilot has access to.
By Steven Perry 810054
#515664 Tomer, I had this problem as well. PMDG rebuilt the installers at the beginning of July and now it is working again for me.

It does require a uninstall, fresh download, and reinstall though.

Give it a try.