DNS Cache or Router Issue Causing Inconsistent Results on Dynamic Websites?

Hello everyone,

I'm trying to troubleshoot a strange networking issue and I'm wondering if anyone has experienced something similar on a NETGEAR router.

The issue only appears on websites that generate personalized results after a user submits information. Static pages load normally, but on certain dynamic websites I'm seeing inconsistent behavior between devices connected to the same network.

One example I'm using for testing is:
https://calcolaascendente.it/

The reason this site helps during troubleshooting is that every request generates a personalized result based on user-entered birth data. Because the result is unique for each request, it becomes very easy to notice when something is not being processed or loaded consistently.

What I've observed:

• Desktop and mobile sometimes produce different loading behavior.
• The first request can be noticeably slower than subsequent requests.
• Refreshing the page occasionally changes the response time.
• Some users on the same network report no issue at all.
• The server itself appears responsive when tested externally.

Things I've already checked:

• Browser cache
• DNS provider changes
• IPv4 vs IPv6
• Different browsers
• Different devices
• WiFi vs mobile data

My suspicion is that either DNS caching, router-level filtering, or a network optimization feature may be affecting how dynamic requests are handled.

Since websites that generate personalized outputs, such as birth-chart tools, zodiac wheel generators, ascendant calculators, and similar applications, rely heavily on real-time processing rather than cached content, even small networking delays become very noticeable to the end user.

My questions are:

1. Have you ever seen NETGEAR DNS cache behavior affect specific dynamic websites?
2. Are there router settings that could delay the first request while later requests become faster?
3. Has anyone identified IPv6-related issues that only affect certain websites?
4. What would be your first troubleshooting step to determine whether the issue is DNS, routing, or WiFi related?
5. Are there any useful NETGEAR diagnostic tools for monitoring DNS resolution times?

Any advice would be appreciated.

Thanks!