Open Cart - 3.2. Good Coder needed fix cashe, check out, reduce site RAM

We have a site that works well but recently we had developer speed it up so it loads ok on the phones and desktop. He did ok job but later we noticed that whatever he did to speed that site up now few things does not work. Everything worked well before he speed it up....so no problems before. ------------------------------------------------------------------------------------------------------------------------------------------------ There is something in a header of the code that blocks the cart and cashe...so I am sure someone who knows what it is will be a quick fix. This site never had checkout/cart problems. Worked ok all the time, so it is not the check out. -------------------------------------------------------------------------------------------------------------------------------------------------- GOOD OPEN CART CODER NEEDED TO FIX THE ISSUES 1. Site takes so much RAM 520 or something this needs to be reduced. It will blow it out out of the server, runs slow. 2. CASHE PROBLEMS - this site does not clear cashe since now we have issues as: - clients cannot log into account (returns to the same log in screen over and over) - when products added to the cart, then we view cart (products gone) - when we see products in cart, we try to delete it - does not delete - clients cannot check out at all. Related to cashe - delete the products from the site (does not work) refresh the site (so we can see how many vistiors - does not work) remove the images from products - delete - does not work). So basically any live changes on the site are not updating, check out included. The site works when we phizically clear browser cashe - then we log in and it works - but what visitor clears the cashe none stop. Not operational at all. ---------------------------------------------------------------------------------------------------------------------------------------------- We need someone really good to fix that cart, fix the cashe and reduce RAM and improve the speed. He added some code to speed it up. Works ok but site freezes, check out does not cashes out, does not work - he blocked something for speed but must be necessary option since now it does not work.