Same problem over here. Since DCS World JTAC got stuck from time to time playing A-10C.
I can only repeat my last msg over and over.
What helps for me is radio JTAC to end the JTAC missions.
After JTAC confirms the checkout you can call him again and try to re-get the mission.
But this workaround costs a lot of time...
Btw: I managed (by chance) to fullfill a stucked mission once, receiving a "Target destroyed" from JTAC and got offered a new mission. Maybe this information helps someone finding the bug