There has been at least one instance of the incorrectly sized pin being inserted in the forward suspension bar attachment. The two aft sets of pins are a smaller diameter than the front ones. In this case, the error was discovered on the ground when collective was raised/power applied and the crew experienced a "clunk" as the bar lifted in it's bracket, the MGB effectively nodding up and down as power was applied and removed..
I'm not saying this has happened here. It may be possible that the correct pin has been inserted and has failed (not sure how likely that is to happen) or the correct pin has been inserted and the two nappy pins have not been fitted to preclude it slipping out. Yes it is subject to inspection after the installation, but if the incorrect pin can be fitted and no-one notices............
To inspect this pin, a panel on the firewall needs to be removed. Awkward to get to as you need to reach in under the RH engine, in a contortionist fashion to remove the panel fasteners.
I'm not saying any of this is likely or probable, but it is certainly possible. If the failure is a maintenance one.