As per this post: https://forum.snapmaker.com/t/u1-firmware-v2-0-0/43287/40
The movement up/down controls on the U1 control panel move the bed up or down intuitively.
However, it has been reported that the same controls via the Fluidd interface act as if moving the print head rather than the bed, in other words the down arrow moves the bed upwards, and the up arrow moves the bed downwards.
The same thread explains that Fluidd can be configured to mimic the control panel, but it would be best that it did so by default.