Apparently we keep on running into this issue once in a while. While developing you run your objects from the Objects Designer and with each single execution a new Windows Client session is being fired. Using your valuable time and frustrating your debug session as the previous one is not valid anymore and you have to start a new one. If I recall this right it first happened when NAV 2013RTM and R2 were installed side-by-side and we got a fix for that from MS.
In the meanwhile I didn't get bugged by this until a couple of weeks ago after I created a new Azure machine for NAV 2016 which contained CU 3. As I was busy preparing various courses and needed my time for that I didn't allow myself to fix the issue, somewhat annoying my students, with every other object I launched from the development environment. Triggered by this old post showing up in my dynamicsuser RSS-feed subscription (another annoying phenomenon), and having some time today, I decided to get this thing solved for my NAV 2016 CU 3 installation.
The old post was too old for my issue, but from this I got to others. Through NAV RTC is opening for each run of object I eventually bumped on this one that helped me out fast and easy. Thanx Chris et al.
To prevent myself from having to search again next time this small blog post.