If you enabled sticky sidebar option then it’s sticky when you scroll down. There is no space to show the whole list of brands in the sidebar. You will be able to get the bottom part of the widgets brand only if you get the end of the page https://gyazo.com/1adcc636afb1ca49dd953a24805f3480
So, I would suggest you either to disable sticky sidebar in the Theme Options > Shop or reduce the height of the brand widget scroll to 210px for example instead of the 350px 3ac7ab0b2f3bd9f87d5dcfe2a2723339
