We have @ 150' of chain followed by 200+' of 8 plait.
Every winter I remove the chain to 'wash' it. Washing is dropping it in a bucket while spraying it with some anticorrosive spray (CRC, etc). The chain is still clean with no rust and 10yrs old.
We anchor like you in the same conditions and depth.
I didn't see you mention a swivel, which we have, that not only doesn't twist the chain but provides for the anchor to be retrieved without being upside down and rolling over as it hits the bow roller.
We use a Mantus swivel (https://www.mantusmarine.com/mantus-swivel/
). I remove the large bolt at the shackle to separate the chain from the anchor. I figure the it won't hurt the swivel to get some anticorrosive sprayed on it.
Don't know if it is the washing, the swivel or a combination, but we've never had a twisting issue with our chain.