These comments reflect my experience on a university-level P&T committee, and are relevant to any field where co-authorship is normative, not just econ. Here's a link to a blog post where I provide more detailed comments & advice on the pursuit of tenure:

At the point of tenure review, the hope is that a faculty member will have achieved “scholarly independence.” Meaning, you are conceiving your own research questions and formulating your own strategies to answer them.

If you continue to co-author with former mentor well into your asst. professor years, the concern is that the mentor is still calling the shots. That the mentor is the one formulating the research questions & the strategies for answering them.

In the review process, the goal is to closely examine your research record to find an inflection point: a moment in your career where you turned definitively away from the agenda you pursued under the watch of your mentor(s). Where you declared scholarly independence.

One of many remarkable things about Esther Duflo's intellectual relationship with Abhijit Banerjee: the record shows it was the student, in this case, who inspired an inflection point in the career of the mentor. Banerjee, trained/published as a theorist, broadened his portfolio.

Moral of the story: if you're an asst. prof. deciding whether to continue collaborating with a former mentor, ask "who would be taking the intellectual leadership role? Would this next project be seen as a continuation of my mentor's agenda or of the mentor following mine?"

If you're worried that continued collaboration would create concerns about your scholarly independence, you might want to put that collaboration on hiatus. Once you are past the tenure hurdle, incentives change & you may find an opportunity to renew.