but there is no profile for the whole VIOS machine, Virtual I/O Server
although it is very similar to HMC
This is why i asked you if you use a HMC - you don't, but use IVM instead.
The IVM screen says the total system memory is 16GB. Do you have all 32GB activated? IBM usually delivers its machines configured for CuOD (customer upgrade on demand) and you can use only a part of what is physically installed until you buy a license for the rest.
Did you check the error log? Maybe some memory/memory controller is broken and was deactivated by the system. Have you checked the ASMI?