I have had this plant for several years. Within the past couple months I noticed a few leaves yellowing, but lately it has accelerated greatly to where about half have fallen. I water regularly and keep the soil moist. The pot is large and does have drainage holes. I stopped watering about 2 weeks ago to let the soil dry out but that hasnt seemed to help. This year I have noticed earthworms and centipedes in the soil if I dig around.
Awesome!
The other thing might be the amount of sun it's getting. My pepper plant leaves start to yellow and fall when they're getting too much sun. I recently moved them to a shadier part of the yard and the yellowing has definitely decreased.
Only other thing I can think of is Temps. My hydrangea plant is absolutely hating the super hot weather we've been having lately and dropped more than half its leaves also. Not much you can do about that outside of moving it inside if its potted.
Sorry just going through all the issues I've had that were similar.