Ubuntu – gnome-shell 3.26.1 constantly uses 20-30% CPU

I upgraded from 17.04 to 17.10 on my XPS13 9360 and have, as others, tons of issues. This one now is that the process

/usr/bin/gnome-shell

has a way to high CPU usage of constantly between 20 and 30%:

PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                     
2026 xxxxxx   20   0 4264020 703284 315308 S  29,6  4,3   9:32.37 gnome-shell                                                                                                 

The used version is

$ gnome-shell --version
GNOME Shell 3.26.1

This happens directly after booting the system with nothing open except a terminal running htop (beside some startup apps such as Dropbox) but clearly no heavy graphics programs.
I don't know where to start, here are some information about my graphics card

$ lspci | grep VGA
00:02.0 VGA compatible controller: Intel Corporation HD Graphics 620 (rev 02)

$ glxinfo | grep -i render
direct rendering: Yes
    GLX_MESA_multithread_makecurrent, GLX_MESA_query_renderer, 
    GLX_MESA_multithread_makecurrent, GLX_MESA_query_renderer, 
Extended renderer info (GLX_MESA_query_renderer):
OpenGL renderer string: Mesa DRI Intel(R) HD Graphics 620 (Kaby Lake GT2) 
    GL_ARB_conditional_render_inverted, GL_ARB_conservative_depth, 
    GL_NV_conditional_render, GL_NV_depth_clamp, GL_NV_packed_depth_stencil, 
    GL_ARB_conditional_render_inverted, GL_ARB_conservative_depth, 
    GL_MESA_window_pos, GL_NV_blend_square, GL_NV_conditional_render, 
    GL_OES_element_index_uint, GL_OES_fbo_render_mipmap, 

Please let me know what else I should post in order to trace this issues — many thanks!