Wrong Memory is displaying in task manager for Default and Named instance in Sqlserver
Perhaps you have Lock Pages In Memory for the &quot;active but low memory&quot; instance? Task manager only show a minuscule memory usage in this case. You can for instance look in the error log file (startup info) if lock pages are used.
So, there's nothing to &quot;fix&quot;. You should look at the memory usage through something else then Task Manager. For instance sys.dm_os_process_memory (physical_memory_in_use_kb) or sys.dm_os_sys_info (committed_kb)