The phrase "acting up" means behaving badly or causing trouble, especially in children or pets. It can also describe a device or body part not working right or showing symptoms.
I wanted to tell people, "My depression is acting up today" as an excuse for not seeing them, but I never managed to pull it off. Ned Vizzini
My cholera's acting up again. Libba Bray
I was studying to be an architect, I wasn't plotting to join the movies. Films were just another career option. I took acting up with the same schoolgirl enthusiasm I had for examinations. Acting is a job and I take it very seriously. Aishwarya Rai Bachchan