Residential router interfering with SRV records

Question

My situation:

I have an application (Minecraft) hosted on a dedicated server that uses SRV records to direct application-specific traffic to that server. The server has been hosted both on site (at my house) and on a cloud VPS, with both locations having the same issue with a client's specific router. This is all a personal hobby setup by the way.

The DNS records are setup so that there is a CNAME record defining a subdomain subdom1, an A record defining a subdomain subdom2, and a SRV record that points my application (on subdom1) to a specific port on subdom2. Basically:

subdom1.example.com -> subdom1.example.com
_minecraft._tcp.subdom1.example.com -> subdom2.example.com:portxyz

This setup works for every client that has connected on a wide range of different network setups (both residential and commercial) except for one client who is connected via a residential router (which is a Netgear WPN824N, connected by either Ethernet or WiFi).

I have narrowed down the issue to this specific router using three methods.

1. The client is able to follow the SRV record and connect to the server when the computer is connected to a different network, so it's not an issue with the computer hardware, os, or client software
2. The client is able to follow the SRV record and connect to the server when bypassing the specific router and connecting directly to the modem, so it is not an issue with their modem or ISP
3. More than one computer with known working clients has been tested, and none of them were able to evaluate the SRV record when connected to this specific router.

This issue has existed for over a year now.

The question:

I would like to understand better how SRV records work, and how something like a residential router can cause a SRV record to not be followed. And short of telling the client to connect directly to subdom2.example.com:portxyz, what particular settings on a typical residential router might fix this behavior?

tl;dr What settings on a residential router could cause a SRV record to not be followed? (And how do SRV records work in general?) This issue is only being seen with a single router.