Ugh... I think we've all been through this :( I so see one big blob on the lower right of the frame. Can you try to shoot something really 'bright/white' ? That will let you see all the nasty!
Hope you're able to resolve this easily. I have 'gack' that seems to just 'come & go'. Very Frustrating! Good Luck!!
I had a major sensor problem in the summer. There were greasy spots on the sensor and when I tried to clean it myself thinking it was dust I spread the grease over the sensor. A professional clean was needed. The chap in the shop told me that using my 100-400mm lens added to the problem as it was like a bellows and if I was changing my lenses outdoors - which i do quite often I was getting pollen in and onto the sensor and that is greasy. £60 later - all sorted. It will of course happen again I expect as I do change lenses when out. Good luck sorting yours out.
Hope you're able to resolve this easily. I have 'gack' that seems to just 'come & go'. Very Frustrating! Good Luck!!