Error: PING 2620:fe::fe(2620:fe::fe) 56 data bytes
│ From fe80::1e7e:e5ff:fe3f:e718%eth0 icmp_seq=1 Destination unreachable: No route
I am using Allo USBridge Signature with a DigiOne HAT
I saw a post on the dietpi forum about a known problem with a change of update URL which will be fixed soon. Can’t find the post to share though sorry.
I had a similar problem, which I solved by uninstalling and reinstalling Roon Bridge using dietpi-config.
If it helps, I think my problem is a difference in kernel version between dietpi installs. I have more than one RPi and the most recent one is on a newer kernel version for the same version of dietpi. The newer one is the one I have a update issue for Roon Bridge.
Isn’t such better suited on the DietPi forum or GitHub? 
However, Destination unreachable: No route means most likely there is no IPv6 standard gateway applied/default route, often the case if the router does not send out (sufficiently regularly) router advertisements. Check:
ip -6 r
It should contain something like
default via fe80::xxxx:xxxx:xxxx:xxxx dev eth0 proto ra metric 1024 expires 148sec mtu 1492 hoplimit 64 pref medium
A default route to the router’s local link IPv6 address with an expiry usually up to 1800 seconds. The router needs to send out router advertisements to update this route within 1800 seconds accordingly. If this isn’t done reliably, check router settings, or otherwise disable IPv6 on the DietPi system. Can be also done right from the error prompt menu, which I guess you saw this error on.