"Twisted Myrtle" sounds like a film noir role. One of those grainy, black & white, poorly shot movies. Or maybe a character from a board game, Twisted Myrtle, in the garden shed with a bulb auger!
I think that species is of Mediterranean origin so it should be fine with high pH soil, although 8 is pretty high. That's higher than the soils in my area and we're known for our caliche! With two common types of chlorosis to choose between I'll take a guess, based on your high pH, that iron chlorosis might be the one you need to watch for.
"Improper watering" ....now there's a catch-all phrase!

Yes, I know "improper watering" is a catch-all phrase.
It is a Mediterranean plant. A type of Myrtle with a neat growth habit.

I wonder if there is a soil borne pathogen that could cause chlorosis? This would be quite different than true "iron chlorosis".

Little John Bottlebrush is a type of Myrtle that has been planted around San Antonio.

We have had lots of rain (10 inches this month) and all of these cute Bottlebrushes are turning a horrible yellow. I just don't think this is the same as "iron chlorosis" that we have in the Southwest. But I know that in Arizona they treat Bottlebrushes with iron, but I don't think iron will save the San Antonio Bottlebrushes...

I hope I'm not confusing anyone...LOL