This issue occurs if the virtual machine generates data faster than the consolidate rate. For example, asynchronous consolidate starts with a 5 minute run, then goes to 10 minutes, 20 minutes, 30 minutes, and so on. After 9 iterations, it goes to 60 minutes per cycle. During these attempts, consolidate is performed without stunning the virtual machine. After max iteration, a synchronous consolidate is forced where the virtual machine is stunned and a consolidation is performed.
Note: Snapshot consolidation time varies depending on the type of machine and environmental variables, thus it is difficult to estimate a completion time.