CIBSE Gain results can often display Solar Gains at night, for example:
The CIBSE Gain calculation considers both an instantaneous solar component and mean solar component. The mean solar component consists of solar gains that are re-radiated from surfaces having being absorbed as gains during the sunshine hours.
The Cooling Plant Operation in Building Data determines the hours that these gains are considered. Therefore, if you have set your Cooling Plant Operation to 24 hours a day, the gains for each of those hours will be displayed in your results, as above.
For example, the effect of changing the Cooling Plant operation to 6-19 hrs can be seen below:
Detailed information on the calculation method and algorithms used in the CIBSE gain calculation can be found in the Design Database manual.