We recently upgraded Jenkins and accurev plugin (from 0.618) and have failed builds due to the workspace not being populated correctly, actually not populated at all in some cases, only updated.

Build is done on an explicit workspace and on a specific location on disk. If I have no changes in SCM and no workspace or host change from the last build, there is no pop being done. IF my workspace is missing files or if I cleaned it after the last build, I do not get any file on disk and the build fails.

The problem was not there in 0.618 where all workspace logic was in AccurevSCM.java.
The functionality is now in AccuRevWorkspaceProcessor.java which does not do a pop on the workspace (as was done before) by default. pop is only done on host change or workspace move.