Well this is strange and it drives me close to remove elementary os all together.
Last night I issue apt install gimp then go to sleep. The next day I woke up, everytime I launched an application from the dock (its name is plank) or from terminal, it won’t show up on dock but is represented by a new, ugly, low resolution icon on the dock. I tried to google to no avail until I decide to check my /var/log/apt/history.log and saw that the last package installed is gimp.
I quickly do
apt remove gimp && apt-get autoremove to undo it and everything work normal again after log out. I still don’t know what caused the problem, at least I was noted that those are the packages removed along side with gimp:
gimp-data libamd2.3.1 libbabl-0.1-0 libblas3 libcamd2.3.1 libccolamd2.8.0
libcholmod2.1.2 libgegl-0.2-0 libgfortran3 libgimp2.0 libilmbase6
libjavascriptcoregtk-1.0-0 liblapack3 libmng2 libopenexr6 libsdl1.2debian
libumfpack5.6.2 libwebkitgtk-1.0-0 libwebkitgtk-1.0-common