Is this thing lubed, heavily?
The two things I bolded above. That's not even possible. If you have the correct VLTOR tube(s) - there are two you can get, and one that's wrong.
The UTG Pro you bought before was 7" internal depth, and I verified that with them on the phone - it's all they make. That's AR15 Carbine Receiver Extension, right there, only.
It's not possible for you to have a VLTOR A5 tube that's only 1/8" more in internal depth. Something bad is going on here.
The two VLTORs that with work correctly are the VLTOR RE-10/A5SR. That's a six-position tube. Then, you can use the VLTOR RE-A5. That's a seven-position tube. Which one did you buy, directly by model number?