Poor UMG Slider Performance when Windowed in Shipping Build

I noticed a strange quirk when doing things with click and drag in UMG while the game is windowed, and it only happens in a shipping build. It appears that, when either the mouse cursor is visible, OR the mouse is not captured to the viewport, a very low precision click and drag detection is used.

For moving the camera around a character in a menu this is easily avoided by setting Hide Cursor During Capture to true. For a slider, this is overridden with the cursor always visible causing the low precision mode to be used all the time. The result is a very laggy slider that is impossible to be precise with.

As for why this doesn’t happen in the editor: my theory is because the editor is running maximized in the background and overrides the windowed game.

Some more findings on this. It appears to be resolution dependent, not so much windowed vs fullscreen. Also, it only affects sliders, spin boxes are fine.