According to the SMBIOS specification (revision 2.7 or newer), the extended module size field should only be used for sizes that can't fit in the older size field. Also, extended size should store value in megabytes.
Memory Device — Extended Size:
Bit 31 is reserved for future use and must be set to 0.
Bits 30:0 represent the size of the memory device in megabytes.
According to the SMBIOS specification (revision 2.7 or newer), the extended module size field should only be used for sizes that can't fit in the older size field. Also, extended size should store value in megabytes.
Memory Device — Extended Size:
The problem was detected while trying to boot guest macOS which inspects SMBIOS tables. Bhyve has already been fixed: https://github.com/freebsd/freebsd/commit/dd589c9906a9b7819a21ffb6d7a00a090be32f55