You need to keep all the version "referenced" in your wyserver.wys files.
In your case you need to keep the updates from 39 to 40 (masl.39.to.40.wyu) and the fallback (masl.all.to.40.wyu)
.wyu files
Hello everyone,
Could you help me?, I need to know if its really necessary to have all the .wyu files on the ftp path or I can delete it and leave only the new .wyu of an update.https://ibb.co/evjvJG
The selected range for build the updates is the past version to the lastest version" (see the attached image)https://ibb.co/mnD0kw