Read the warning message and follow the instructions to find and renumber the duplicated prefixes.

The Tutorial explains how to use the Design Manager.

The issue is there are NO duplicated prefixes in the schematic!

please export your design as EasyEDA format to support@easyeda.com
we will help to check.

You need to check other pages, the prefix must unique in the project pages/.

Suddenly all schematics elements get duplicated for unknown reasons (and each element placed over the same element, so duplications are not seen)

@krlf,

Please at least post some screenshots or the url to a public project that demonstrates this issue.

@krlf,

If you can reproduce this issue, please post a Bug Report about it with supporting information as suggested above.

Thanks.