For me the problem was the landscape loading in after character spawn. If you use level streaming or world composition.
To fix it you can wait for the level to finish streaming in:
In the level blueprint on BeginPlay event block player input and deactivate gravity. Then delay for 0.1 and then do FlushLevelStreaming. That way the character floats in the air until the level is streamed in. For some reson it only works with a short delay befor FlushLevelStreaming.
Did the trick for me, at least.