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The client capture contains ICMPv6 "Packet Too Big" frames (filter: icmpv6.type == 2) containing "MTU: 1492". The server side does not.
So the maximum MTU in the network path is 1492 bytes. The value 1492 suggests that there is a VPN or tunnel in between. PPPoE maybe?
The TCP-SYN from the client shows a MSS of 1440. Thus MTU = 1440 + 40 (IPv6) + 20 (TCP) = 1500 bytes.
So a transmission fails when full packets are send (no fragmentation for IPv6 possible), like a large query. Small queries will pass.
Quick fix: lower the MTU of the client. Better fix the MTU in the network path.
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