1995 F150 locking hub problem

Have a 1995 F150 with 83k with manual locking hubs. Haven't used them in almost a year. Today turned them to LOCK, normally very stiff, but this time easily turned with two fingers. Front wheels would not engage. Local mechanic put it on a lift, manually switched each hub from LOCK to FREE several times and they work fine now.

Any idea what would cause this? Have never had this problem before, always worked great. Thanks in advance.

if it realy cold outside. sometime to much grease in them will cause it not to engage or because it has not been engaged it had harden grease in the hub engage them and drive around awhile get them lubed up or take them out clean them up and re grease them lightly to take them out remove the cover and there is a snap ring use a skinny screwdrive to remove it

Think you've hit the nail on the head. They're working fine now, but hadn't used them for a year, will know better next time! Thanks...Art