I travel a lot and I swear I've never seen the same shower design twice. There's so many different freakin' ways to deliver a stream of water to your head and they nearly all require some level of finessing. I'm assuming it all stems from an 1800s court case about patents but fuck that judge and everyone involved that day
It seems that hotels somehow always install the most obscure and convoluted shower designs. I've never had too much trouble with showers in people's homes, but every time I shower in a hotel room I feel like I'm trying to operate an oddly temperamental steam engine.
In the house I grew up in, you’d also have to hope no one flushed the downstairs toilet. If so, the cold water pressure would suddenly drop, leaving a lot more hot water coming out of the shower head.
If yours uses a thermal sensing element (not just mixing blind),I've found running it through its full temperature range helps a lot. I suspect limescale and other crap build up on the thermal element. It adds several years on to the life of the mixer. Descaling it would likely also work, but involves removing it from the pipes, to get the cleaner in.