The external water pressures on plate elements above the soil are not determined correctly in PLAXIS 2D AE.00 when:
See also the image below.
This issue is now solved in PLAXIS 2D AE.01
A workaround for this issue in PLAXIS 2D AE.00 is to create a dummy soil cluster at the side where originally no cluster is defined. Then in the phases, make sure to deactivate this dummy soil cluster.