Drop shadow much stronger in export than workplace

[Daniel23370421sl9h]

When I work on this overlay the dropshadow looks good, but when I try to export it, add a background or look in the preview, the thickness and darkness of the dropshadow suddenly changes.

(closeup from in the workspace normally)

(closeup from the export preview)

(When I add an background to the workspace)

Preview


I noticed that gradients also change when I suddenly export and I really don't know why. 

Do I have any setting wrong or something?

[Earth Oliver]

You can never judge transparency against the checkers, so either add a solid fill in your layers or change the setting in Prefs to show white in the background.