It’s actually not blocked. If you’re requesting content from this domain, it’ll succeed (and there will be a record in the Visited tab).

There’s something wrong with the DNS record for this domain. DNS query reports non-existing domain (NXDOMAIN) after the IP addresses are returned. And the last NXDOMAIN record causes the router to add a failed record in the logs.

$ nslookup s.srvsynd.com 1.1.1.1
Server:         1.1.1.1
Address:        1.1.1.1#53

Non-authoritative answer:
Name:   s.srvsynd.com
Address: 18.204.98.216
Name:   s.srvsynd.com
Address: 18.205.232.214
Name:   s.srvsynd.com
Address: 34.231.4.204
Name:   s.srvsynd.com
Address: 34.236.210.83
Name:   s.srvsynd.com
Address: 34.226.87.209
Name:   s.srvsynd.com
Address: 18.204.190.178
Name:   s.srvsynd.com
Address: 35.168.165.225
Name:   s.srvsynd.com
Address: 18.206.31.91
Name:   s.srvsynd.com
Address: 54.156.10.4
Name:   s.srvsynd.com
Address: 52.54.19.1
** server can't find s.srvsynd.com: NXDOMAIN