General iOS 9.3 support PDF sync in iBook, but how do I get this to work?

[striders]

I want to be able to sync PDF files added to iBook across all my 3 devices (MacBook, iPad and iPhone). All iOS devices running iOS 9.3.3

I have followed all the instruction to enable Cloud syncing in iBook:

• iOS devices: Settings -> iCloud -> iCloud Drive —> Enabled
  I can put files into iCloud folder in OSX and it will show up in my other iOS device
  
  
• iOS devices: Settings -> iCloud -> iCloud Drive -> iBooks -> Enabled
  
• OSX: System Preferences -> iCloud -> iCloud Drive -> Enabled

All books purchased from iTunes (not PDF files) are synced across all 3 devices.

However, PDFs files are NOT. I have tried adding PDF in OSX and they don't show up in iOS devices. I tried adding PDF files in iPhone, and they don't show up in the iPad or OSX.

Did Apple removed this capability? How did you get yours to work?

 

[striders]

UPDATE: this is interesting. When I posted this, I did a test by adding a PDF file from my iPhone (downloaded from a website then click "Open in iBooks"). That PDF file never show up on my iPad or MacBook.

Fast forward to now (about a day later), that same PDF show up in my iPad! This is truly bizarre!

I'll be checking if that same PDF show up in my MacBook when I get home.