Forwarding maintainer's response to aur-requests as it has not been received/accepted by the mailing list.
MarsSeed [1] filed a deletion request for cloudstation-3.0 [2]:
I suggest this Synology Cloud Station legacy version
from 2017 can be deleted, if there are no objections.
[1] https://aur.archlinux.org/account/MarsSeed/
[2] https://aur.archlinux.org/pkgbase/cloudstation-3.0/