The guys above are correct, anything quad screen and above will show a sub stream, this is correct for local monitor and iVMS software to help manage decoding performance. You can change these settings and some others things to check -
1)Local Monitor - Menu/Configuration/General - check resolution setting for monitor being used, ensure it is as high as the monitor can handle.
2)Local Monitor - Menu/Record/Parameters/SubStream - check resolution setting for sub stream and bitrate
3)iVMS software - by default the software will automatically select the sub-stream on anything more than quad display, but you can manually correct this and control it to whatever you want. Tools/System Configuration/Image - un-select 'Auto Change Stream Type'. Now if you right click the folder under Main View, you will see the option to select Main/Sub Stream for all cameras, if you right click on the individual camera in the folder this is by single camera. depending on if you are already viewing cameras, you will have to stop and re-select the camera stream for it to take effect.
One final thing make sure the resolutions setting from the camera are also the expected resolution (max for the camera) and bitrate.
And as always ensure your firmware is upto to date on cameras and recorder.
Hope this helps