All maintainance work after initial base edge set and polish should be done on side edge only.
Have you or did somebody plane the side walls.? this may or may not help.
I am not a fan of DMT's I use Moonflex Diaface stones.
Some chewed up edges need to be reset with a file.
When resetting my side edge. I first back-file with a 7 degree guide and a panzer file.
Then again using the panzer file I use 1 degree over the final side edge angle I want to achieve until I have a nice sharp edge tip to tail.
I would then finish with a fine or finer file set at my final bevel angle. Notice NO TOUICHING the base edge. I would alos highly recommendu sing base tape during this process.
Now I would start with a diamond or a series of stones depending on how much time you want to spend and how polished you want your edge.
The process of finishing the side edge is designed to continually smooth out the previous work, leaving you with a nice smooth, grippy edge. I like to make a few passes with a middle grit diamond file next, of course attached to the file guide. This will really soften the rough effect that the file has left. At this point in a new ski prep, I will take an Arkansas or ceramic stone and lightly pass it along the base edge to cut the "curl" of steel that has developed from all this filing. I usually do this freehand, with light to medium pressure. Now you are ready to really put the edge on – use your Arkansas or ceramic stone with your file guide, and begin working the side edge steel back and forth until it is extremely smooth and sharp. A light no pressure pass at a 45 degree angle with a hard gummi block will finish the edge off, and you should have a very sharp, smooth edge that is ready to ski