I didn't know that there were any grp Sagittas in Australia (from your email address I assume that is where you are). Please tell us more, like how it got there? and when?
I assume it is a S African built boat. Many of those were owner completed and so may not have been built according to plan.
In any event, the rigging should be tight enough so that it doesn't appear slack until sailing to windward in 15-20 knot winds. It shouldn't ever be considered as "flopping around".
Those who have my MSHMF video will have seen a shot of the lee rigging on our Sagitta where it does indeed flop around. That was because the film was taken on one of our first sails and before the riggers had come to retune the rig. (Rigging always stretches when new and has to be re-tensioned after a few sails)