Certified GKH Gardening Expert
It is likely a pollination issue, especially if it's been unseasonably hot in your area as this makes it more difficlt for pollinating insects. You may need to hand pollinate.
I have same question regarding pineapple guava not thriving. Mine are in full sun, and have been planted a year now--all are on drip system. Only a few have lightly flowered and none have borne fruit. Also, the color of leaves are ugly light gray-green with yellowing on some leaves.