Seems to be a response like this in every thread related to actual football this season. Whilst I agree that on-pitch matters aren't at the forefront of our minds - isn't it nice to just talk about football for a change!
I think conceding early can simply come down to lack of concentration, leading to individual errors and poor shape. I do think that fatigue and lack of rotation affects this though as a fresher starting 11 would potentially be sharp from the first whistle, rather than having to slowly warm into the game