Wipe (Fade/dissolve) is not working

Hi there! I am testing the new mlt7 version of kdenlive, built from git 2021-06-27.

When overlaying one clip on another on the timeline, and adding the "wipe" effect from the quicklink on the timeline, The wipe effect appears, but does not seem to have any effect.

I have tried with high and low quality composting, and timeline preview and a quick render. All show a straight cut instead of the fade (dissolve) that I was expecting.