This is an issue with your levels/lacing. The tagging node you are inserting a list of 2 revit instances and a longer list of elements.
Instead of flattening the list of elements, keep them in two separate lists based on linked instance and then adjust the levels of both inputs on the tagging node.
I have been reading it, but… how to put it… have trouble projecting it on my question.
(In the link / example mostly numbers and points are used instead of text).
Pointers on my own graph or examples are waaaay more helpful to me instead walls of text.
(like an example of how to Instead of flattening the list of elements, keep them in two separate lists).