https://www.strava.com/activities/245207108
22 miles this morning. 16mph average, so not as quick as I'd like for a flat ride like that. I found out why when I got home - I'd got my cycling socks on the wrong feet. 10W lost right there. Definitely nothing to do with the wind or being woefully out of condition after winter.
You can't judge fitness gains/losses by average speed - there are too many variables.