PiHole fails to update (v481->v520)

I am trying to update PiHole, but when the update “finishes” (that is, the “loading” screens disappears), I still have the older version installed.
I did not manage to understand what happens by looking at the logs, sorry. I just sent them through the ‘Settings->Support’ web interface.
Thank you very much for your work!

Not sure if it is the issue, it complains about:

Apr 09 14:07:02 syncloud pihole.ftl[13252]: dnsmasq: failed to load names from /var/snap/pihole/current/config/pihole/custom.list: No such file or directory
Apr 09 14:07:02 syncloud pihole.ftl[13252]: dnsmasq: bad address at /var/snap/pihole/current/config/pihole/local.list line 1
Apr 09 14:07:02 syncloud pihole.ftl[13252]: dnsmasq: bad address at /var/snap/pihole/current/config/pihole/local.list line 2
Apr 09 14:07:02 syncloud dnsmasq[13252]: using nameserver 2620:0:ccd::2#53
Apr 09 14:07:02 syncloud pihole.ftl[13252]: dnsmasq: read /var/snap/pihole/current/config/pihole/local.list - 0 addresses
Apr 09 14:07:02 syncloud dnsmasq[13252]: using nameserver 2620:0:ccc::2#53
Apr 09 14:07:02 syncloud dnsmasq[13252]: using nameserver 208.67.220.220#53
Apr 09 14:07:02 syncloud dnsmasq[13252]: using nameserver 208.67.222.222#53
Apr 09 14:07:02 syncloud dnsmasq[13252]: read /etc/hosts - 7 addresses
Apr 09 14:07:02 syncloud dnsmasq[13252]: failed to load names from /var/snap/pihole/current/config/pihole/custom.list: No such file or directory
Apr 09 14:07:02 syncloud dnsmasq[13252]: bad address at /var/snap/pihole/current/config/pihole/local.list line 1
Apr 09 14:07:02 syncloud dnsmasq[13252]: bad address at /var/snap/pihole/current/config/pihole/local.list line 2
Apr 09 14:07:02 syncloud dnsmasq[13252]: read /var/snap/pihole/current/config/pihole/local.list - 0 addresses

Do you need to upgrade your existing pihole settings?
You could try removing pihole and then install fresh latest.