You possibly need a rear bag main body.
The reason it is cutting out when you pull it back is loss of electrical connection that usually leads us to one of two possibilities:
When you pull it back the electrical terminals in the bottom of the handle shaft can be losing connection as you pull back. This is because of a hairline crack in the main body where the triangular aluminium tube goes into. This is caused by either/or or a combination of wear and tear, old age, the machine being dropped or not carried correctly
The other possibility as you suggest is wear or breakage in the bottom of the main body causing a disconnection in the electrical terminals there as its pulled back. Wear to the pivot point on the arm arm that comes out of the base or in the electrical plug there can also be a culprit too. Click the main body off and examine the components there and see what has excess wear or play and go from there.
If the fault isnt obvious after inspection as above, it might be wise to bring it in if local, or send it in for repair