Missing space on Fusion Drive (partition problem)
Starting with OS X 10.11 (El Capitan) you'd have to enter a distinctive (> 0) size to execute the resizeStack command. The magical ... 0g doesn't work anymore.

But in your case the resizeStack option is the wrong one because your Logical Volume Group already occupies almost all available space on the Fusion Drive:

Total disk space: 1240 GB
LVG size:             1239 GB
PV1 + PV2 size:   1239 GB
LV size:                  616 GB

The resizeStack option is appropriate if you want to resize the LVG and all subsequent Core Storage items (like the LV, PV and LVF).

Here you just have to expand your Logical Volume to completely fill the LVG with the following command:

diskutil cs resizeVolume lvUUID size


In your case that is:

diskutil cs resizeVolume 7EE2FE6D-3D37-46AA-B948-52243490F324 1239g


If you get an error (not enough space...) choose a slightly smaller size like 1238g.



After further investigations one have to state that the Fusion Drive is corrupted:

Boot to Internet Recovery Mode, destroy the LVG, rebuild the Fusion Drive and restore your Time Machine backup: here is a how-to. Start with 'Rebuild Fusion Drive' (recommended if you have a Time Machine backup).