In the modeling mode, and then cube grid tool, Shift+Click to complete a block selection across two cells is removed in 5.8.
Now you have to drag to create a rectangle. Makes it a lot harder to prototype levels,as you now have to get the camera into a posistion where it can see it cell A & B.
Previously you could select cell A, then move the camera and then shift+click on cell B and you would get the rectangle. Takes lot less time to do, and made it so I would do less mistakes using it.
What Type of Bug are you experiencing?
Level Design & Art Tools
Steps to Reproduce
Open modeling mode in editor, then select cube grid tool, select a cell, then shift+click on another cell on same z level.
Expected Result
In previous versions, click on cell A then shift+click on cell B would fill a rectangle between the cells.
Observed Result
Now it just selects the object your mouse is at. No cell selection.
Seconded this, and others have similar issues in the Unreal Source Discord. I notice a lot of suspicious commits in InteractiveToolsFramework/InputRouter.cpp which seem related to this bug, and my humble efforts of debugging point to the culprit being some modification done there for 5.8.
I hope this gets fixed, since it render CubeGrid practically unusable compared to my previous workflow.