Resizing Size-Values by Better UI does only work if the Canvas Scaler is set to "Constant Pixel Size". The other modes would fight with Better UI resizing and should therefore not be combined with Better UI. Note that the other modes are not necessary as long as you do positioning work with Anchors (See Snap Anchors Window)
Since version 2.5 this limitation is communicated to the user with options to fix it:
It can happen that the Resolution Monitor (and Materials) reset to default values when upgrading the Unity version of an existing project or deleting the Library folder.
Make sure you have a backup of these files before upgrading unity / deleting the Library folder and replace the files with the backup afterwards (or with version control: simply discard the changes in these files).
The "Override Screen Properties" may not update their children outside of play mode. Select the current resolution again for the game window to update it.
Some Material Modes (e.g. Additive) may look strange or even doesn't work.
Fix A: sometimes the references to the materials break. Relink them automatically:
navigate to Assets/TheraBytes/BetterUI/Runtime/Resources
Delete the "Materials" scriptable object
It will be automatically recreated with correct references when accessed the next time.
Fix B: Some settings in the materials are not applied by Unity. Force Unity to apply them by hand:
Try to fix it by opening the material in the inspector (found at Assets/TheraBytes/BetterUI/Runtime/Resources/Materials) (For example Standard_Additive)
Click "Combine Alpha" and "Combine Alpha" again (so that it has the same value as before)
Change the "Alpha Clip Threshold" value and change it back (if it is a material with "Force Clip" enabled)
References break in a parent prefab when "Make Better" is used inside a nested prefab. Research has already been done to fix this. Right now it seems like it cannot be solved but further research will be done. The references have to be re-assigned by hand.
In a prefab scene the resolution is not updated when changed in the "Pick Resolution" window, if the game window is in the background. Therefore, the UI is not updated properly. To overcome this, either have the game window always visible or change the Screem-Configuration-Settings of the "Pick Resolution" Window and disable "Apply Resolution" there. Then the selected screen configuration is simulated - also in prefab mode.
If you are using Unity 5.4 or 5.5 (or even earlier), the scenes might not be loaded correctly if you support different screen types. Change the resolution after loading a scene to fix this.