1. for quicker checking, the "Bond Force" output data item may also be of your interest.
2. Thank you very much for careful checking and reporting the problem. It looks like the problem is really related to the long "through the air" segment, where the bond stress gets interpolated from the 2 ends. We at least need to better explain this in our documentation (Troubleshooting, 22.214.171.124.2 Unrealistic bond stresses along unbonded segments)!
As the solution suggested there can not be directly applied in ATENA Egr 2D, I only see the following way:
I. Add a small elastic cube or triangle around the bar, just underneath the end of the bonded segment.
II. End the bar inside that triangle.
III. Create another bar, with perfect bond, from the endpoint of the above bar, till the original bar end in the "wrap".
The problem is that if you make the distance from the surface too short, the extremely short bar segment brings extreme stiffness differences in the model, resulting in numerical problems. Something like 1/2 of the element size in the concrete should work.
Fixing a node of the triangle in horizontal direction helps to avoid unrealistic horizontal displacements.
I am sending my model through email such that you can look at it and make further modifications.