Aye, to clarify the suggested max. for the luggage rack is something in the single digit kgs, can't remember exact number. The strength of the sub frame mounting to the main frame can be addressed by the stronger bolt fix you mention, but the issue of the weak subframe itself is a different issue (the C model has a different rear subframe that the A model which deosn't have that issue).
We were initially somewhat surprised by the low weight rating on the rear luggage rack and guessed that it was primarily related to the rack itself, but after having mounted a normal weight rack with panniers (that had some weight on the sub frame as well as on the main frame) it became abundantly clear that the sub frame is limited in how much weight it can handle and it will crack.
I don't have the bike in front of me, but by memory the top tube of the rear sub frame extends rearward beyond the point where the bottom support comes up to meet it and thus you have an unsupported tube beyond that point. Weighting that tube will cause it to stress to the point of breakage.
It's an easy workaround, you just have to ensure that the your lugagge rack is bolted to the main frame for the front portion of the rack and NOT bolted to the subframe at the back, but instead all the rear weight is carried by the support bar that runs down to the rear foot peg.
I see you are in Libya. Must be an interesting place to be workig at the moment. Did you bring your bike or not quite safe to be wandering round yet?