Your biggest problem here is Wifi for your core. A server client based system like Roon isn’t going to perform well in this scenario Roon recommend to not have your Roon core which is a server on WiFi for good reasons as they understand how demanding their software is and how inadequate wifi is for a server to be connected by. Endpoints are generally fine.
You mention Roon having diagnostics but have you tried diagnosing yourself by removing WiFi and add in a cable as a test to see how it performs? It’s simple to achieve temporarily. This would be the first action point I would do in any network related situation, remove the weakest link.
With WiFi issues it’s not always an issue with WiFi bandwidth. Whether you can stream 4k over WiFi is irrelevant as the process and chain in that scenario is very different to Roon. If you only have one WiFi point this can even more of an issue especially if you have lots of other devices on your WiFi network all cramming to be heard and pull data.
WiFi can only send or receive to one device at any one time and then it’s not simultaneous. The more devices on a network the more they all try and communicate and keep airtime to the access point . All other WiFi in your local area from neighbours also adds to this airtime as they take it from you if on the same channels. All this adds latency. It’s all at microsecond levels switching between which device gets data which receives data but it’s all latency and this adds up and data that is sensitive to time related clocking such as Audio suffers.
Roon pulls over WiFi from internet for a Tidal stream , Roon has to send out that stream back out over WiFi so your endpoint can receive it. WiFi endpoint passes it on to endpoint. This all has to go through the same access point that then sends it on to your endpoint. Thats 3 WiFi hits taking valuable airtime with an increased risk of packet loss and then all those needing resending. This adds more latency.
Netflix as an example is pulling directly from the router via WiFi to the device it’s running on. One WiFi hop, less latency and Netflix buffers a lot and also has adaptive streaming to cope. Latency here isn’t so much of an issue, you can skip a frame or to and most people don’t notice.
There is another thread all about this that covers why WiFi for core is a bad idea. Follow peoples recommendations and you will have a much better experience.