There are issues with multi-cursor replace and CSS variables.
If you Cmd + Shift + L on normal CSS properties, you can replace them easily.
If you do the same on a CSS Variable Prefix, then it starts to get squirrelly.
You can also do it with dragging to create multiple cursors:
The code that was diffing a change from the updated DOM text was getting confused by the way the replacement occurred twice at the start of the replaced range but also directly after it. That, in turn, prevented the change from being properly applied to secondary selection ranges. This patch should help.