Hello and and thank you for your question. For over 34 years, I have answered questions just like yours. And I look forward to assisting you.
When you first start receiving SSI, the payment center sets up payments based on when your claim was processed. And in your case, it was the third Wednesday. But after a few months, your case is reviewed and formally placed in the system. Likewise, the date you get payments is based on your birthday. As a result, your payment was readjusted to the 4th Wednesday. Sorry. I know this is confusing and unfair. But the SSA makes the rules, even if they are dumb! Thanks for understanding.