I have been experiencing this bug where the control centre refuses to scroll down after a certain point in the ubuntu mate 18.04.1. But I'm able to see all the icons when control center is maximized. Also, the bug vanishes after logging out and logging in.
The workaround: change the window width away from just before it wants to add a column.
And for reference, the discussion here.
between can you guys tell me how to add a picture in the forum, I'm new here
Just drag & drop the image into the message. It will be shown in the preview panel.
alt-print screen > copy > paste works as well.