First, make sure a ball or something like that is not under the slide.
Did that, was a bear to get out.
You need to also check the roller or slide rub block under the front end. Some can be adjusted or may need to be replaced.
With the slide out. Check angle of the slide wall, front and back. Are they the same? If not, check for loose bolts letting the floor sag and the top not come all the way in.
On Edit...I forgot to say look for somthing stuck on the slide top holding it from closing. Even with a slide topper, stuff can blow in there. Even the slide topper can get out of adjustment and jam.
