The  icon next to instances on the instance list and the instance retention graph, which lets you view object values, may be disabled and show this tooltip:

Instance values can be unavailable for several reasons:

• You selected Make snapshots faster by leaving out object values when setting up the profilng session. 
• The snapshot grew bigger than 4GB.
  Snapshots are limited to 4GB in size for performance reasons. If a snapshot grows bigger than 4GB, ANTS Memory Profiler prioritizes collecting reference data. Object values are dropped from the snapshot to make space for reference data.
• The object or array has no values or is empty.