Merriam-Webster defines "in tandem" as
1 : in partnership or conjunction
2 : in a tandem arrangement
Based on the definition of tandem,
(a) a bicycle for usually two people sitting one behind the other
(b) 2-seated carriage drawn by horses harnessed one before the other
"in a tandem arrangement" would give me an image of two things aligned one after the other, not aligned in parallel. Therefore, for "events happen in tandem", I would imagine that events do not happen at the same time but one happens after another.
However, Cambridge dictionary defines "in tandem" as
at the same time
Thus, the statement of "events happen in tandem" would indicate two events happen concurrently, not one happening after the other.
Is the term "in tandem" an ambiguous term ? Is "in sequence" or "in order" a preferred term to describe events happening not at the same time ?