It's a bug... workaround is to move Peripheral Variables into ECC variables. At least that is working for this customer.
CSCts40575
Symptom:
After upgrading 7.2.1 to 7.6.3 Agents no longer get Enterprise Variable Data- While call is reserved the variables are populated correctly but when call connects the Enterprise Data Variables clear to N/A
Conditions:
Issue is seen when CAD is upgraded to 7.6.3 version
Workaround:
None