The right way is some sort of inline water flow sensor, so it’ll trigger within seconds of you turning on the shower to warm it up. With an esp32 and a sensor, and some clever use of the sleep function, it’d probably last a year or so on a couple of AA’s.

Low effort and price tech is probably better in a wet environment though! If you just want the mood lighting, get a wireless button and stick it somewhere near. Tap it on, tap it off!

If you want to feel that automatic magic, consider a cheap battery powered temperature sensor. If you fix the chassis to the shower head pipe it’d probably be accurate enough. Also, assuming you need to wait for your shower to heat up, you’d have a pretty good idea when your shower was hot too - when it triggers your automation for the lights!

Just make sure the sensor polls often enough or can be made to report on a significant temperature difference in a timely fashion. Something like this might do it: https://sonoff.tech/products/sonoff-zigbee-temperature-and-humidity-sensor-snzb-02p

Also avoid WiFi for buttons, connection and addressing takes ages and sicks for an instant response needed for something like lighting changes

tl;dr:

If you think something is blocking DNS traffic, you could try configuring DNS-over-HTTPs or DNS- over- TLS and picking a reputable upstream. This should obfuscate the traffic somewhat and get past common DNS interference issues and tactics.

So building on what yourself and everyone else has said, it does seem to be a DNS issue.

I found that at select times my local ISP was up to shenanigans with DNS.

I live in a very small country and work in IT. The NOC for all three ISPs and I have met. It would surprise me if they were competent enough to do this intentionally for malicious purposes.

If you can get access out to the internet via ping, see if you can do other things - get on a VPS and test with tcpdump at both ends. There’s a few free ones or trials great for disposable purposes like this. Set it up in advance…

You won’t know what it is til you troubleshoot.

I’ve had huawei firewalls reaching some simultaneous connection limit and fail, reversing their ruleset - blocking everything except ICMP, tr069 and ssh (concerning) outbound…

I’ve had problems with specific DNS servers, through the ISP’s network.

I’ve seen regular BGP changes causing outages all over the place (the ISPs locally don’t peer with each other…)

Post your findings, would love to help/hear!