The host operating system may be running out of sufficient resources for the Engine to perform its tasks. The numbers supplied by the system indicate the current usage of memory by the Engine service against the Low Working Set Limit configured for the Qlik Engine.
Example after startup:
Information WorkingSet: Configured Working Set Size is 4.200-5.400 GB (setting 70%-90%)
Where 70% is the (default) Low limit, translating to 4.200 GB.