Depending on how big an area yu have to deal with, it might be better to cut out the offending strip and replace it with a thicker one.

Cut back to the nearest frame if you can. Otherwise, cut out an area a foot long or longer.

You can use a utility knife to slice through a strip that is thinned. Move it in a straight line, parallel to the glue line, and a little inside that. You want all your cutting to be on the strip that will be removed. Just use gentle pressure and keep going over the same line as many times as it takes to cut through.

Once the thinned strip is removed you can use sandpaper to clean up anything that remains from the strip and also clean up the glue line. A little heat from a heat gun, and a scraper may help with removing the old glue, or just sand it patiently. A rasp might be a good tool here, too.

Install a new strip and procede from there with your sanding.

hope this helps.

PGJ