First, please don't be alarmed by my thoughts below. I'm a structural engineer (not a naval architect/engineer) and these are some things I would check.
Check every bit of the compression posts down to the bottom at the hull. It seems to me that you could have one of the following possibilities:
1.There is corrosion that has weakened the compression post causing local buckling of the post walls, or a base plate is corroded, or the compression post has buckled, either of which could result in a shortening of the post and the deflection you see at the base of the Mizzen. Check the hull where the compression post rests with special care looking for fiberglass cracking.
2. The rig could be so extremely overtightened that it is bending the entire boat. This could have happened in the past resulting in damage that your current tightening has exacerbated. There is tension in the forestay and backstay pulling up on the ends of the boat, the masts push downward resulting in the fore to aft bending of the hull (imagine a giant with his thumbs where the masts are and fingers at the end of the boat, pushing with his thumbs). This is a load the boat is designed for, but it is possible to overload anything. This seems a very remote possibility but does account for your report of things not lining up that did in the past. Have you made any hull, bulkhead or deck modifications?
3. The shrouds may be overtightened which would result in bending of the hull athwartships, but that seems much more unlikely to cause the observed damage than #2.
The sternward rake of the masts (both of them?) could be problematic. It would be helpful for those here who know more about adjusting the rig than I if you measured the rake. Perhaps someone else could advise you on this. Check the message history for Beaute Olivier on Oct 20, 2015 in a thread titled "Spreader Cracks" for some guidance on where the mast should be.