Hi Keith,
welcome to TFP.
there are lots of reasons this could happen. Most notably chemicals. There are all sorts of pool products on the market that can and will clog up filters.
Also, imporper water balance provides a possiblity of calcium deposits in filters.
So ultimately, I would think that something you are putting in the water is causing this issue which is chemically reacting with other stuff and clogging up your DE. As a note, Phosphate Remover seems to be somewhat notorious for clogging filters.
Us here at TFP use a regimen of water management that only allows for minimal additons of chemicals and only when accurate testing of the water shows what the water actually needs. And we base our methodology on science and chemistry instead of the sales pitch from chemical makers and other folks like pool stores that have financial interest in the mix. As a result, us TFPers dont have experiences like yours.
If you are interested in having a TroubleFreePool with minimal expense and effort, then click on the Pool School button at the top of the page. There is a ton of great info available.