I picked up my first native in September

Repotted a week later with bonsai mix from the nursery and slow release for natives


It sits in full sun and a drip tray but as of late has some yellow and is dropping leaves


It's probably due for a prune, but for now, could there an issue here?
Research online says could be 2 things
1. You’ve added uncomposted organic matter into your soil;

2. Your soil has an iron deficiency, too much phosphorous, or the pH is wrong.

Thoughts?
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