Preview blinks after annotating in PDF

Hi everyone,

I am a fun of preview over other apps. However, recently a blinking problem almost let me giving up Preview. The pdf file works well in Preview before I add a lot of annotation (text). However, after a lot of annotation, the screen start to blink, only in the region of the Preview.

I tested multiple PDF files, all have the same issue. The same problem equally exists whether Preview is in full screen or not, when Preview always has the sidebar or without it.

Another issue is that the Text annotation does not allow you to type continuously on different parts of pdf. It is very annoying to click text box every time I need to annotate it.

I hope Apple can resolve these problems.