Illustrator keeps saying 'applying art brush' and loading after every single action I make.

I am attempting to create an illustrated poster in adobe Illustrator 2025. The illustrations are of some simple flowers but are composed of lots of lines with a rough texture art brush. 

I illustrated the first three flowers without issue and everything was smooth. Then I come back to it to draw the fourth and suddenly it is like trying to wade through treacle. Illustrator brings up a small window saying 'Applying Art Brush' after every single action I make. Wether that's toggling a layer visibility, selecting an anchor point with the pen tool or anything similar. Moving an anchor with the pen tool takes several seconds to calculate and update. 

I also created a flat coloured square shape behind the flower illustration with no stroke applied, however it seems to be glitching and has applied the artbrush I used for the lines in the illustration as a stroke around the shape. Nothing I do to the shape will remove it and when I create a new shape it has the same issue. 

I have closed and reopened, illustrator, and shut down and rebooted my computer to no effect. 

Illustrator seems to be using 80% of memory. I have no other programmes running, I have plenty of space on my hard drives.... 

Can anyone tell me why this is happening and if there is any way for me to resolve it?

I have attached a screenshot of the project in question.
The artbrush used is the 6th brush down on the list (The thin one between the two larger chalk brushes). The lines don't have many anchor points on them either. 

Any help would be greatly appreciated. As working with this is incredibly frustrating and time wasting.