Failed to move from 7.7.6 to 7.7.7 missing SASSAddonImportFileCreator

Initially trying to go from 7.7.3 to 7.7.7 but that failed so i moved to 7.7.4, 7.7.5 and 7.7.6, all working fine.
When finally changing pom-file to 7.7.7 (all parameterized) i get the error below.
There is nothing in the release notes for 7.7.7 that indicates any to do, to my understanding.

Anyone encountered this and solved it?

Thanks.

[INFO] --- vaadin-maven-plugin:7.7.7:update-theme (default-cli) @ the_app---
[INFO] Updating theme VAADIN\themes\powertender
[ERROR] Error: Could not find or load main class com.vaadin.server.themeutils.SASSAddonImportFileCreator
[ERROR] Updating theme "VAADIN\themes\powertender" failed