Have a similar issue with my 2017 76 series wagon and hayman reece bar. 12 bolts secure the bar to the 4x4, 5 on each side, 2 underneath and 3 to the side, and 2 attached to a bracket in the middle. Twice now the 6 side mounted bolts have sheered off both sides and the 4 others underneath on the sides have all-but shaken loose. Same problem trying to fix the issue, the welds holding the nuts in place have let go and it is impossible to get new ones in there without removing panels. Had to weld a piece of wire to the nuts to hold them in place while we put new bolts in last time. Couldn't get any spring washers in there so the nuts ended up coming loose and couldn't tighten them much. What a rubbish design.
Tried going back to Toyota but since the bar isn't Toyota branded they wouldn't help.
So now stuck in Mt Isa waiting for a new towbar to be delivered since the old one is now cracked and broken from the stress of not having properly tighten side supporting bolts.
Not sure how the boys at TJM Mt Isa are going to fix this one but at least they are willing to have a go.