In the same context, I have come across the usage of 'discussion' and 'discussions'
We thank abc and xyz for useful discussion
We thank abc and xyz for useful discussions
Is one of them more correct than the other?
They are both grammatical, and in most cases interchangeable.
Discussion is one of those words which can be a mass noun or a count noun. As a mass noun it means the act of discussing in general, as a count noun it means a single event of discussing. So for useful discussions implies that there were several separate times at which you discussed. For useful discussion says that you have discussed, but contains no implication as to whether this took place once or several times. (The third possibility for a useful discussion is explicit that you only discussed once).