Sleeping outside

This morning when I went to my chickens I noticed they were all soggy wet. They have a coop in a fox proof run plus access to a portion of the garden when I let them out. I don't close the pop hole except when it is very cold so they can get out to the feed and scratching area as early as they want. I was a bit late going to close the gate on the fox proof run tonight so it was dark. I found all three chickens sleeping/roosting ouside in corners of the pen rather than in the coop - this is probably how they got so wet last night. I picked them up and put them in the coop - and I did close the pop hole. They had layed an egg each in the coop during the day.
Can anyone explaine why they had chosen to sleep out side?
Thanks

Have you checked for red mite in the coop or lice on the chooks themselves? Red mite is a really common reason for them not to go into their coop at night. I've never known lice to cause the same issue as the red mite only attack at night, causing the chooks to associate the coop with the mites, whereas lice live on them so they generally feel uncomfortable wherever they are.

If you do find red mite, best stuff I found was washing out the coop thoroughly with poultry shield, and the regular (and continued) use of diatamaceous earth (diatom powder) in their nest box, rubbed under the perches and into the ends of the perches, and brushed into every crevice of the coop. Also sprinkled into any shavings you may have under their perches, and also on the chooks themselves (vent area, underside, under wings - careful of eyes and beaks). Once I had lice and managed to get rid of them with the Poultry Shield, I never got them back whilst using diatom powder.

Thanks - I will look for red mite and get some treatments for them if I find any. Do I remember that you rarely see red mite during the day so best to sneak out at night with a torch to find them? Do I look for anything on the chickens themselves - such as red rashes on their legs or something?

slide a white piece of paper into any nooks and crannies in your coop and if you have redmite your paper will be smeared red. Another place they often lurk is in the part of a door near the hinges. If you find them then thoroughly cleaning and treating every week will be necessary. At their worse they can kill a broody hen or a young or weak hen