In our last hybrid, that was starting to happen in ours. The cause was the cable was a tad too long, causing too much strain on the bunk fabric, especially in the corners. The cable in our Aerolite that supports the bunk had 3 adjustment holes on the bracket to make the cable shorter or longer. I un-bolted the bolt on the bracket inside the RV and moved it to the next hole. That raised the bunk a 1/2" but also relieved the tightness on the bunk fabric.
Now to your issue, I called Aerolite and they forwarded me to their company that makes their bunk material. For $125 they would resew the "J" channel back onto the bunk fabric. I would call whoever makes your trailer and ask who makes your bunk end fabric.
I didn't want to remove mine, as the cracking was only about 3/4". I glued mine with a automotive emblem glue or Shoe Goo that is flexible. Here is a picture of my tare, before I applied any glue. 2005 Aerolite hybrid