Losing Layers when saving as PDF from CC 2018 and reopening in CC2017.
We save all our ai files as "Illustrator Default" PDF's so we can see the layers in Acrobat and come back and modify the file in ai with no concerns. After updating to CC 2018 and saving a file the same way making sure to preserve illustrator and create acrobat layers when opened in an older version of ai (CC 2017) we will not see the file with layers. If opened in 2018 all is good. Never had this issue with CC 2017 when someone opened it in an older version. We send out a lot of files this way and has been an issue since updating to 2018. If saved as an .ai file it is fine but it should work as a PDF also as it did in the past.

Any ideas...