Ok. so, I got an error on upload. No watermarking on the photo I tested.
Also, the preview in the admin shows the text, but not the overall PNG pattern I uploaded (which I've attached).
You have to enable the option "Start Watermarking" in the main plugin configuration to enable the watermarking for all the users in the front end.
What happens if you change the watermark png image for another?
You will not have any problem if your watermark image is 1960px * 1960px, if you get any other issue, please let me know and I will answer asap.