The more I look at it the more convinced I am that it is to do with the new lowering links. I say this because both the chain and sprockets look in reasonable nick with no appreciable tight spots, the chain sits on the sprocket fairly tightly with only a small about of movement when you lift it.

Maybe after being on the centre stand for a while the shorter links cause the linkage to stick and only free up when the bikes moved around for a bit?

I did have a session in the garage today but of course it's not playing ball now and I couldn't get the chain to tension up!!