Issue:You have combined network license, which consists of PD Collection 2018 and Plant Design Suite Ultimate 2018 network licenses and see that Inventor 2016 takes a license from Plant Design Suite Ultimate license a head of PD Collection license.
Causes:Inventor 2016 will take Plant Design Suite license ahead of Collection, as in 2016 there was no Collection licenses.
In 2016: Cascading Sequences for Autodesk Products PD Collection is not even listed.
However, with Inventor 2017 and 2018 Collection license will be consumed first and then the suite license as documented.
2017: Cascading Sequences for Autodesk Products
2018: Cascading Sequences for Autodesk Products
Solution:To work around this issue, you need to create an options file to control access to Plant Design Suite Ultimate 2016 features.
For various ways of controlling access to a network license via options file, please refer to Control Network License Access Using an Options File article.