When updating to 6.1, there is a new button in the side panel navigation that is a Collapse All button. This button should be a circle with an up arrow inside it.
For a regular update, all regular themes get updated with this, but all custom themes are missed.
To change the text Collapse All to the circle with the up arrow inside it, add the following CSS to the CSS file associated with the theme:
/*applies to the collapse all button on navigation */
/*the text 'Collapse All' is rendered in the container, so to switch from an image to a text link, just remove the following four lines*/