Magento 2 Pre Order was working well until we found out that it is not compatible with Cart2Quote. We couldn't view the Quotation of module Cart2Quote in the admin.
Pre Order module and Cart2Quote module both use the same block
which causes a conflict between them.
To solve this conflict, we have changed this file app/code/Bss/PreOrder/Plugin/BackendNotice.php
Please check and apply this fixed file on your site.
If you have any issues, please feel free to contact us.
We'd like to help.