hi ! i had this same problem and found (through this https://www.reddit.com/r/computerhelp/comments/1gmbr1p/solution_for_icon_invisible_properties_and_task/? reddit post) that these steps helped solve it
Win + R
type in "regedit"
typically, it will take u to "Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\Shell Icons" automatically but if not then manually navigate to it
double click on the file that is named "29" and delete it
restart ur device
this should fix the invisible icons and the task manager not opening ദ്ദി( ´ ▽ ` )
u probably encountered the problem a while after removing the arrow beside app icons (just like a lot of us lolol)