Fertilize it heavily every week for this season and see if it doesn't explode next year. Some need shock therapy. Been there, done that.

Noting that you are in zone 10, what type of soil? Sandy? Then it might just be a lack of nutrients.
There has been lengthy discussion on this forum recently of root knot nematode and it's my understanding that it is often a big problem in sandy soils. Possibly RKN could be holding your plant back. Do a search here for more reading and try to scratch around and examine some of the roots.