You are using Di-Chlor--that's what Chlor-Brite is. You are using massive amounts and that's releasing the CYA that's shot up in your pool.
It's not strange at all--it's rather expected. The ONLY way you will get the CYA down is to drain and refill.
But if you have a FAS-DPD test kit there's no reason you MUST lower CYA. Switch to bleach and run your FC up to 20ppm until your pool clears. Then maintain your FC in the 5 - 10 ppm range for normal swimming.
Each time you backwash and add water your CYA will come down a little. You CAN lower it all at once by dumping half your water, but you don't HAVE to do that.
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