One thing that was a bit different on that particular session with the 8 m was that I had the bar adjusted from the customary 48 cm to 56 cm wide (because I had been using my recently purchased Apollo 8 m, which is a great kite BTW , and forgot to set it back to 'normal'). But I have a hard time believing that would make any difference…..
Hmmm, if inflated just reasonably, it seems this very kite got this "known" but rare problem - but it would be a lot worse for average and heavier riders
The longer bar does not mean it will "buckle" more, no.
So if not a defect in this very kite (I have a hard time imagining how this could be possible though, but never say never), then everyone having this very model/year/size would have the same problems, even to a bigger extent as most are heavier, I would say
This was the reason I moved away from switchblades. A few times I would collapse my smaller 7M and 9M switchblades. These kites were being used on stronger days and I was not comfortable with their behavior. Yes, they were inflated correctly and I have not had issues with other kite brands. I had no issues with the larger switchblades but this issue was the icing on the cake after a bunch of cabrinha bar complaints.
I haven’t had that issue with my SBs of that vintage. If the kite losing some inflation pressure don’t forget to check the O ring in the inflation valve - a few grains of sand will cause a slow leak that can be hard to find unless you know what to look for. Cold water does not measurably affect kite pressure in my experience.
My two cents:
1) The bar is too long (over sheeted). If you sheet in and the behavior goes away that would confirm that the kite is oversheeted. In that case, find a smaller bar for your 8M/6M. For e.x. 40-45 cm.
2) Pump the kite up rock hard. Most SLE kites are pretty flat, so a lot of force can be applied to the shoulders.
3) Use rear attachment point bridle farther from the tailing edge (closer to front sle)
4) Depower the kite so that it is not oversheeted.
5) Use shorter kite lines. The kite will get through the loop faster. I typically use shorter lines for my smaller kites.
6) Switch to a c-kite.