But the phrase "in tandem with" is accepted English.
That's the joy of language. New meanings pop up and definitions change. Some people are more accepting than others.
There used to be a computer manufacturer called Tandem who made fault-tolerant computers. It was so called because most components were in pairs so there was a redundant backup. Now these components weren't strictly one in front of the other. I expect a few people were keen to point out that because of this "Tandem" was a misnomer.
Incidentally Tandem computers had a banking system called "Internet". For a while the Tandem nerds tried to cling on to the fact that this was the
proper Internet. It was a losing battle and the system was renamed in the 90s.