As described in the CA Datacom/DB Database and System Administration Guide, in the section "Implementing and Maintaining Virtual Library System Files › VLS Files," DDOFILE is
A work file for online Datadictionary. The Datadictionary Online Work File (DDOFILE) stores session dependent information over a logical process which can span the processing of several panels of information. DDOFILE is the default name for the Datadictionary online work file. This name can be changed in the DDOLLIB= parameter in the DDSYSTBL macro. For details on specifying a different name for this file, see DDOLLIB=.
Because it is a work file, and is session-based, every user that enters and exits a DDOL session will cause this file's utilization to grow and shrink. It's size or contents depends on the Datadictionary online activity taking place at that moment. During the online sessions, it is not unexpected to see one value at one point, and then see that the file is much more full or less full minutes later.
The description of the DDOL000047A and 47C message says
When a logical unit of work (LUW) in CA Datacom Datadictionary online is completed successfully, any VLS member associated with the LUW is deleted. However, if the LUW ends with an ABEND, the VLS member remains on the VLS work file until the same user starts another similar LUW. It is conceivable that a series of ABENDS could cause the VLS work file to fill.