I’m definitely not overwatering, and wait for at least the top third to dry out before doing so. It hadn’t been fertilised for around three weeks. Last night I gave half the usual dose of balanced feed after watering. I can’t work out what is happening with it.
Don't panic, but do worry. It is not happy. Iwould water more, but I am not sure which substrate you have this in though...
Check also for bugs on the plant. Spider mites, aphids, thrips. I am not convinced it is the heat. My tree just saw 2 weeks of 30+ celcius and could not be happier. I did water twice a day, and the tree is growing in near non-organic, very open substrate.