Howdy yinichai,
Thank you for reporting this issue. I am going to need a bit of additional information so that I may be able to further investigate. Would you be able to clarify if you are using a Binary or Source version of UE4? What is the exact version that you are currently using? In the second image, what BP graph are you using to Add to Viewport?
I have attempted a quick repro of this issue internally and have been unsuccessful with seeing any errors. Any additional information regarding this is greatly appreciated,
Thanks and have a great day!