Viewing this document, which is still in draft form, the bleed area contains a dark gray horizontal line across the top and a larger dark gray rectangle near the top of the right-hand side. There are no unseen objects in the design that could be causing this.
Peter Crownfield shared this idea
I have been having a similar issue for over a year, through multiple documents and several versions including v17.01 (Mac OS 11 and 12). Random color blobs and lines appear on screen. Sometimes they disappear if I zoom in or out. Other times I have to leave the page and scroll back onto it to see my work. Screen shots from 2 occasions in attachment.