When assigned to "Worker" or "Soldier" outfits, colonists will remove all their gear but refuse to put anything on afterwards. If returned to "Anything", they'll put clothes back on. If a new outfit configuration is created, colonists will dress accordingly. I've verified that Worker and Soldier outfits still show all the same items they should, and those items are available (since everyone just stripped out of them to begin with). So, it seems the issue is specifically with the default outfit configurations.