I didn't meant that, network-manager OR connman as network connect is another topic (and should be optional to the user to pick its preffered one), the issue is about the systray, there's some applications that doesn't shows up on systray, nm-applet is one of them, a systray is very needed for many applications (dropbox, nicotine, xpad, bluetooth widget, kupfer (just in case), and many others...)
I have added a new FAQ entry of why network-manager, just in case people asks why this one or wants to switch to another one 
Why we use Network-manager
it happens to me all the time (after half an hour of using), but is probably my intel card model especifically, IIRC raster told me is related to the xorg intel driver version
My specs:
Graphics: Device-1: Intel Skylake GT2 [HD Graphics 520] vendor: Lenovo driver: i915 v: kernel
bus ID: 00:02.0 chip ID: 8086:1916
Display: server: XOrg 1.20.4 driver: modesetting unloaded: fbdev,vesa
resolution: 1920x1080~60Hz
OpenGL: renderer: Mesa DRI Intel HD Graphics 520 (Skylake GT2) v: 4.5 Mesa 18.3.6
compat-v: 3.0 direct render: Yes
