I googled how to enable Debug Logging, but the log file doesn't seem to show anything related to beds
EDIT:
I found the problem.
I was using a lot of Femshepping beds which count towards bed numbers, but don't allow you to assign them.
I tried copying all the keywords, actions, and the script from the Friffy beds that do work properly, and it nearly worked.
I showed the beds as a resource the needed to be assigned, and even gave you the "Assign" prompt, but hitting enter did nothing.
I got around it by replacing some of the Friffy bed textures of beds I wasn't using with the Femshepping ones, and all is good.
The "which settler which bed" mod was useful in getting everyone assigned to a bed.