The factory used Bostik Vinycol 1520 for assembly. Per Bostik lab testing, the bond should require between 10 to 20 kg of force to unglue a 5cm section. If the bond lets go with less than 10 kg, then the glue is weak and should be redone. (20 daN / 5cm was the max after a 7 day cure, 10 daN / 5cm was the weakest after torture testing in boiling water or after time in a 70C oven).
Sikaflex will not affect the factory bond, but I do not recommend it. It is akin to spraying paint over a rusty frame that has lost 90% of the original metal...covering up the problem won't make the lack of strength go away.
If you can easily peel the joint away without a heating aid, then the joint should be reglued. If you reach a section where when you go to peel it, and it starts to tear the coating from the supporting fabric, then you have reached a well bonded section.
Some edge ungluing is normal. The factory uses solvent for cleanup and it tends to weaken the edges a little, but if the lack of strength is systemic, then the only option is to reglue.
Gluing geek since 2007