Anton Zaides wrote a good post about shadow work in engineering teams. He discovered a senior engineer on his team was spending over 40% of his time on work that didn’t show up anywhere—code reviews, mentoring, ad-hoc support fixes, etc.
This part is important:
The shadow backlog isn’t the problem—in my opinion, that’s probably the work that should have been done in the first place. The solution is to stop doing it under the table and make sure you have space for it. The more people don’t agree with your roadmap because it was decided for them, the more shadow backlog you’ll have.
The shadow backlog is a symptom of a roadmap that doesn’t reflect reality—and that often happens when engineering teams are not involved in planning and prioritization. That is the real fix—making sure everyone understands and is aligned on the roadmap, and making sure this kind of BAU (Business As Usual) work is visible and planned for.