what it means? DROPPED_diskgroupname

I have a Oracle 12c RAC database which has disk groups that have disks in two different storage .

when i analyzed ASM log and i saw that disks in the second storage was dropped one day after installation of the RAC.

when i query like bellow i dont understand what means

_DROPPED_0001_MULTIPLEX

_DROPPED_0001_PDB3

_DROPPED_0001_FRA

_DROPPED_0001_PDB32

_DROPPED_0001_CRS

_DROPPED_0002_PDB1

Because when i normally dropping some disk or disk groups in my test enviroment i never saw result like _DROPPED_diskgroupname

May be you what is this?

select group_number, disk_number, header_status, state, total_mb, free_mb, name, path from v$asm_disk;