Hello Sergey,
Out of the configurations you mentioned above, the only one that should work is when you connect REF to 2.5V. Leaving the REF pin disconnected in an instrumentation amplifier is not a good idea. And you can't tie it to ground (AD8293G80) because it would be outside of the valid range (per REFERENCE CHARACTERISTICS on the data sheet).
Check your connections. Keep in mind there is a 5kOhm resistor in series with pin 4. Pin 6 should also display the same voltage as pin 4.
Good luck!
Gustavo