Where have all my partitions gone?

[AC Question]

Notably, partition number 1? Where has it gone.
The app DiskInfo tells me that I have the following partitions on the internal storage of my Asus Fonepad (K019, running Lollipop 5.0):
* Cache, mounted as /cache, partition number 0
* System, mounted as /system and /local_cfg, partition number 2
* Data, mounted as /data, partition number 3

The missing partition would explain why I have only 0.9 + 1.8 + 3.9 = 6.6 GB on the internal storage, when I should have 8 GB.

So, partition number 1 seems to be missing. Where has it gone? How do I get it back?

Thanks for your time.

 

[Onktebong]

The app Storage Partitions tells me that I have 22 partitions (!) in internal storage.
Of which four, /factory, /config, /firmware and /cache, are mounted.