If the body is wobbly and it cuts out when pulled backwards, then >this<
is probably what's causing the wobble. As a result, the male terminals of >this loom<
sometimes arc and degrade causing the problem you describe.
If you look down into the neck, if that is the case, you will often see one terminal looks shorter than the other. Or looks sharp and burned.
It can be the bag housing internally at the bottom at the female terminal of >this loom<
(where the one above connects to). But very seldom, and you will often see burning if that is the case.
Speaking of the back body, another possibility is will the handle pull out of the back body when the tab is locked? If so, they can crack internally and as you use it, the crack expands, the handle lifts up/out a bit and continuity is lost. In that case, replace >the bag housing body<
Before suggesting a PCB, which might be a more regular issue, it depends on which one is fitted >the older one<
tends to be more reliable than >the later one<
. And also, if a PCB, it will usually cut out predictably, such as 10 seconds after starting for example. If it is cutting out randomly in use, and not if left running alone, and especially if pulled back, one of the first issues is more likely.
However, you say you have checked the lead, but if just a continuity test, that often isn't enough. The cable can fail internally just near the cable entry grommet. In that case, you need to power it up, and pull and twist the flex by that grommet slowly and in all directions to see if you can replicate it.