The calculation of the lateral stability is based on the Eurocode 1992-1-1 in article 5.9.
There are two situations with different limits for lateral stability. The transient and permanent situation can be checked. If the limits are reached over it does not mean that the beam loses the stability, but you should use a higher type of analysis. The higher form of analysis is not implemented in IDEA StatiCa.
Watch the recording of one of our webinars, where the calculation of lateral stability was performed.