What percent of the inside lining of the Instant Pot actually stainless steel? I’ve tried 2 intant pots and both pitted with first use. The 2nd pot I never added salt to the recipe, made the squash soup recipe from the booklet and used vegan liquid buillion and washed pot immediately after cooking, and ALREADY pits have formed! I find this unacceptable. My stainless steel pots I’ve used for 20 yrs have never pitted or corroded even with salt added to recipes. How much stainless steel is used in the lining of the pot?  If no salt is used there should NOT be corroded spots. This is absolutely unacceptable for a promoted “stainless steel” product. I know it’s made in China but is the steel lining like 1% steel? Is there any quality control in the manufacturing? The lining cooks off into the food, I don’t want metal in my food even if some deem it safe.
There is no such thing as a mixed material containing "x percent steel", unless you are talking an inhomogenous composite material (which would be most certainly more expensive than using all steel, and wouldn't look metallic). A metal alloy is either a steel (stainless or not stainless), or it isn't a steel.

There are thousands of stainless steel types (which you could group by 3 major types and a few specialty ones) which have varying corrosion resistance. Also, a major factor here is how the steel was polished/finished.

Have you compared cooking the same dish in another (non instant, non pressure) stainless steel pot? 

Were there any other metal items (spoons, standoffs, immersion blenders...), especially made from something else than stainless steel, more than momentarily present in the liquid while cooking or while the contents were still hot? Stainless steel doesn't like being part of a boiling battery...

A salty, sour liquid at pressure cooker temperatures is actually a rather aggressive chemical mixture - even stainless steel has to work hard here.

By the way, the stainless steel typically used for pots has mostly iron (good for you), carbon (not bad for you), nickel and chromium (technically not good for you)...