Category Setting Disappears After Working For Weeks/Months

I manage two separate WordPress sites and they each have two Syndicated Sources setup where they pull in posts from XML feeds on a regular basis. On each site one of the Sources is set to add a Category or two to differentiate those posts from the other Syndicated Source and the manually created posts. Over the last year, about a half-dozen times, the setting for the Categories to be added has mysteriously disappeared although the rest of the settings for the Source are still there. These generally happen several weeks or several months apart so I haven’t been able to find a pattern of any type. So far, I have just gone in and reset the setting as well as manually finding and tagging the posts that should have been tagged. Do you have any idea what might be going on that would make the setting basically unset itself?