I have the a problem with my HP T620 build.
After adding identical type of memory (from 1 x 4GB to 2 x 4GB), 8GB of memory is recognised in the BIOS, but only 3.xxGB is recognised by OMV 5.
I checked and have the amd64 kernel.
The memory bank is correct. Memtest was passed, and swapping the banks of memory made no difference.
What else can I try?