Here’s a long TuD thread about this topic going back to '09. This topic is controversial and I didn’t read anything conclusive or based in real science about this concern. It shares some of the same controversy that the “anti-vaxers” have with childhood vaccines.
Look up the “post hoc ergo propter hoc” logical fallacy. It simply means that because event A happened before event B does not necessarily mean that event A caused event B. This fallacy in logical thinking is so old that it even has a Latin name!
It’s my humble opinion that you will be more richly rewarded concentrating your time and attention on controlling blood glucose than worrying about the negligible effects of the minute amounts of insulin preservatives.