Captnapi, welcome to the Forum!

First of all, let's talk chlorinators. You say it's a CL220, the 220 is an off-line chlorinator, connected by 2 black hoses to the plumbing - the CL200 (that Ben posted a pic of) is an in-line chlorinator and if the quarter/ obstruction was as the pic showed, you'd lose suction and return action.

Please let me get this straight, you replaced the S244 and the sand?

If everything is fine on backwash or rinse, you are NOT filtering - this leads me to think that there is a problem with your sand or the return side. If you have directional eyeballs in the returns, please make sure that the inserts aren't turned sideways.

I think you'll find the obstruction is in the return side