Resolve "Bugfixes in NLO merging"

Description

what are you changing and why

Test Plan

step-by-step instructions for how someone could verify that your code works (perhaps with a minimal example run card)

Example Result

perhaps a plot exemplifying the new feature; ideally the outcome of the above test plan, or the result of a more involved run

Additional Checklist Items

• I have updated documentation as needed
• I considered if this should be cherry-picked/ported somewhere else (rel-2-x or master), and if yes, opened a corresponding issue or MR

Closes #543 (closed)