My activities repeated itself, holding 2 slots, but when I completed it I received reward as completing one activity. Luckily this didn't last, activities appeared later did't repeat itself. I think this might be a bug :)
This is happening to me now, on desktop and on mobile. I don't know if this was supposed to have been addressed previously, but I figured I would post since some time has passed since this was last reported here.
Edit: This became annoying when it continued to read the duplicates as taking up a slot in the activities available, but only read the satisfaction of the duplicates as one activity. Turning in Catch Fish satisfied only one Activities and so on, so I had much less to work with to get rid of them once I got the additional non-daily 10 Activities repeatable and two Mine Ores. I guess I better mine some ore.