Hello! I'm new to the Bonsai empire so this is my first post.
I bought my first bonsai a month ago. It is a Sageretia Theezans (Chinese sweet plum) and last week I repotted it into a bigger pot. I put it in a shadow for a while so the root system can reestablish itself. After the repot I noticed white patches on the leaves (first and second picture). Maybe they were there before but I didn't notice them. I cleaned the leaves with a wet towel and they went away. But after a few days I noticed them again and the biggest one was on a new leaf. When cleaned, the patch on the spot reamins brown (third picture).
I wanted to check if there are any animals present and I didn't see any under the leaves so I put a paper under the tree and shook it. A small white animal with black stripes fell on the paper (fourth picture). There was only one so I don't know if this is also a factor.

I know this is getting a bit long but I have another question. Some of the leaves are getting yellow and then drop off in a few days (fifth picture). Could this be because it was in the shadow or maybe overwatering?

Thank you very much for the answers.