One client shows no query results on the Web UI, just an error message

[deHakkelaar]

You havn't posted the OS running on the PC.
If its Windows:

"No Internet, secured" on Wi-Fi devices with static IPs when using Pi-Hole DHCP

If Windows clients, check DNS server(s) assigned and DHCP service used with below one: C:\>ipconfig /all [..] Ethernet adapter Local Area Connection: DHCP Enabled. . . . . . . . . . . : Yes Autoconfiguration Enabled . . . . : Yes IPv4 Address. . . . . . . . . . . : 10.0.0.11(Preferred) Subnet Mask . . . . . . . . . . . : 255.255.255.0 Lease Obtained. . . . . . . . . . : woensdag 28 augustus 2019 15:31:51 Lease Expires . . . . . . . . . . : donderdag 29 augustus 2019 15:31:51 …