FWIW, this is my go-to dark mild. I especially like the residual body resulting from the use of Windsor yeast for such a light beer. You may find Nottingham too attenuative.
FYI, I replace the beer out post with these on my first receiving keg. Risk of O2 exposure when I put the post back after the transfer on is pretty minimal - never had any oxidation issues.
https://www.kegland.com.au/5-8-male-x-19-32-female-k-lok-to-corny-keg-adaptor.html...
If you aren’t filtering, your beer out poppet may be becoming clogged. I often experience this problem towards the beginning of the transfer, particularly for heavily dry hopped beers.