What are these holes in my Teddy Bear Magnolias?

These holes started appearing in my Teddy Bear Magnolias. Any ideas?

Initially, I suspected insects, such as caterpillars, but I haven’t seen any around my plants, and the holes don’t seem consistent. I then considered a fungal infection, like shot hole disease.

Any thoughts?

Some background information: – Location: Western Australia – Plants are potted, around 100L each – Previously overwatered for a long time, now reducing watering – Recently applied Scotts Osmocote Plus Organics 1.5kg Rose Gardenia and Azalea Plant Food and Soil Improver – Recently used Advanced Garden Insect Killer – Recently applied Liquid Copper – Sometimes, I apply Popul8 and Seasol