I used automatic mode all the time, but maybe half of a year ago noticed that it became substantially slower. It takes maybe 0.5-1.0 seconds more to update preview window. It forced me to apply noise reduction as the last change, but still sometimes when I want to tweak WB again - it is annoyingly slow with noise reduction enabled.
I found that the problem is in automatic method for chrominance noise reduction. If I choose manual mode and set some values (like 5.0 10.0 10.0 for the respective sliders) - it works fast, preview updates without this additional 0.5-1.0 secs delay when I change WB for example.
I don’t know if it is fixable or is it even worth investigating, personally I’m satisfied with manual mode, but just wanted to inform about the problem.
Below are examples of ‘slow’ and ‘fast’ settings: