I can confirm, that there is a bug with updater in Turris MOX (as stated first by @bakuka in Opkg in stable 7.0.0 uses hbl instead of hbs):
Downloading https://repo.turris.cz/hbl/mox/packages/core/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_core
Downloading https://repo.turris.cz/hbl/mox/packages/core/Packages.sig
Signature check failed.
Remove wrong Signature file.
Downloading https://repo.turris.cz/hbl/mox/packages/base/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_base
Downloading https://repo.turris.cz/hbl/mox/packages/base/Packages.sig
Signature check failed.
Remove wrong Signature file.
Downloading https://repo.turris.cz/hbl/mox/packages/cesnet/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_cesnet
Downloading https://repo.turris.cz/hbl/mox/packages/cesnet/Packages.sig
Signature check failed.
Remove wrong Signature file.
Downloading https://repo.turris.cz/hbl/mox/packages/luci/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_luci
Downloading https://repo.turris.cz/hbl/mox/packages/luci/Packages.sig
Signature check failed.
Remove wrong Signature file.
Downloading https://repo.turris.cz/hbl/mox/packages/node/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_node
Downloading https://repo.turris.cz/hbl/mox/packages/node/Packages.sig
Signature check failed.
Remove wrong Signature file.
Downloading https://repo.turris.cz/hbl/mox/packages/packages/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_packages
Downloading https://repo.turris.cz/hbl/mox/packages/packages/Packages.sig
Signature check failed.
Remove wrong Signature file.
Downloading https://repo.turris.cz/hbl/mox/packages/routing/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_routing
Downloading https://repo.turris.cz/hbl/mox/packages/routing/Packages.sig
Signature check failed.
Remove wrong Signature file.
Downloading https://repo.turris.cz/hbl/mox/packages/telephony/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_telephony
Downloading https://repo.turris.cz/hbl/mox/packages/telephony/Packages.sig
Signature check failed.
Remove wrong Signature file.
Downloading https://repo.turris.cz/hbl/mox/packages/turrispackages/Packages.gz
Updated list of available packages in /var/opkg-lists/turrisos_turrispackages
Downloading https://repo.turris.cz/hbl/mox/packages/turrispackages/Packages.sig
Signature check failed.
Remove wrong Signature file.
As can be seen above wrong repo is used for packages: https://repo.turris.cz/hbl/mox/
Seems this needs to get fixed with next version @TomasZak