With nwdr15.img and recently with nwdr14.img I observed same desktop issues on two different Raspberry Pi models 3B+ and 4 and two different screen displays models.
These issues are not present on latest RaspBian distro september 2019 with same 4.19.93 kernel and all applications updated.
First issue is with screen blanking. I had to disable it in preference menu for it was impossible to recover a display after it was blanked. Sometime unplugging the UDMI plug could recover a normal display but usually a reboot was needed.
Second issue is with File Manager desktop icon. When clicking on the icon it opens a file window very briefly and close it right away. At the same time all desktop icons disappear for a brief moment and reappear on the desktop.
73 de Bernard, f6bvp