For me this happened right after updating to Xcode 11.2 (11B52). It started using 100% CPU, which remained even after restarting my MacBook Pro 2018. Force-quitting Xcode several times, helped, then it happened again on the next day. I'm using a Swift projet with Storyboard.
I tried contacting support (case number 100943719734), but they told me they only assist with account maintenance and creation.
I'm prety much tired of the poor quality of Apple software and being forwarded from one place to another without any solution or way to reach the engineers.
I have the exact same problem, the process is mobileassetd and starts when any playground file is opened, takes 70-80 or more % CPU and the fans go crazy. Playground is also incredibly slow (takes 10s to run a print statement).
I'm using XCode 11.2.1, Catalina 10.15.1 on a MacBook Pro 2015.
Haven't found a solution yet, would really appreciate some input!
How much ram in that MB? How much free space on the SSD?