Since I have never had any problems with my slide toppers and the arm you are talking about I cannot speak to that as I did not know it could be locked, however it may be made that way in order to remove the topper and keep it rolled up.
I can see no reason that whatever happened with the topper has any relation to the bed pulling away from the wall. My unit was in the repair shop where I purchased it to have a "field repair" done due to frame flex. The bedroom slide was removed which meant the bed frame was detached from the slide at the shop. On our first trip out after these repairs when I extended the slide the bed stayed where it was and the slide went out. I suspect the frame was not put back in correctly and the "few" screws that actually hold it to the slide wall had pulled out.
I also found that on each wheel on either side of the frame the screws had come loose and the wheels had turned causing additional stress when extending the slide. I added an additional support and used longer screws to attach the wheels.
I removed the entire bed frame and took it into my workshop and basically rebuilt it. Very crappy workmanship in it's construction. I reinforced the part that fastens to the slide wall and also the attachment point where the wheels are mounted, I also added screws to the the part of the frame that sits on the slide floor, there were never any in that and moving the bed frame relied on a total of 6 screws into the slide wall, they did not even hit a stud in the wall just the wall itself.
Here are a couple of pictures of part of what I did to beef up the bed frame and it's attachment to the wall.
Hope that helps with the bed frame problem.