Hi Amir Bar-Maor, Gert Van Maren,
just to report that yesterday I downloaded (deployed, downloaded, extracted) the solar calculation solution.
I ran the analysis for a dataset and everything was fine.
This morning I opened the last project of yesterday, created a new scene, connected a new folder with a new dataset, and when I tried to open the same task I got the error message and the red exclamation mark.
I solved by extracting the same package in another location, open the project, exporting the task to a .esritasks file and imported in my project.
It looked totally random to me as nothing has changed during the night.
(solution deployed and downloaded yesterday, so I guess the last available version - ArcGIS PRO 2.2.4)