Problem:
Delete old data from database

Solution:
You may would like to try the following plugin:
- https://wordpress.org/plugins/advanced-database-cleaner/

That will help you to remove orphaned custom fields and there are many more features.

Relevant Documentation:

Problem:

Link two posts within a Many-to-many relationship multiple times

Solution:

You can connect the same two posts only once with the same post type relationship.

As a workaround, you can setup two one-to-many relationships to replace the many-to-many, for example:

https://toolset.com/forums/topic/many-to-many-relationship-w-multiple-child-records/#post-2366553

Relevant Documentation:

Problem:
Impossible to assign user author to a post in edit post screen

Solution:
This is a known issue to us and we already fix the issue but its under going testing and fix for this issue hopefully will be publish with the next release of access 2.8.13.

Here is the errata you should follow:
- https://toolset.com/errata/cannot-set-post-author-when-post-type-managed-by-access/

Relevant Documentation: