An Azure service for ingesting, preparing, and transforming data at scale.
I am not aware of the reasons that caused this issue, or even the details of the issue but the one quick and effective workaround I implemented was to create and use an additional IR. I used a different region just in case the problem was with regional resources.
So although my ADF is deployed in UK West, I created a new IR in West Europe, and this is the one that works.
Hope this helps.