This may or may not affect all users, but I found an interesting bug (I have alerted Axure Support) that I wanted to share in case anyone else is running into this.
I work in a Mac environment (OS 10.14.5, 2018 Macbook Pro) with multiple monitors.
Recently I was working on a prototype that required the use of placing images in a repeater. I went to right click the cell to import and image and the right click option did not work.
I move my Outline, Style, Interactions, and Notes panes to my center monitor side by side so I can navigate quickly between them. It appears that doing this causes the right click to not work with a repeater cell at least in the Mac environment.
Go to View, Reset View. The restores the right click functionality.
Apologies if this is a known issue to the community, just my attempt at being a helpful human being.