The AISC 360-16 code check is considering incorrect value of Cw for non-General UPT sections and non-Isections (WF, S, M, HP types) like Channels when the following conditions co-exist
For the above situations the software is incorrectly considering the Cw value used to check the last General UPT sections or I-section (WF, S, M, HP types) and using that for the other section types. This is causing the LTB checks to be incorrect for the other section types.
There are a couple of workarounds which may be used
The defect is being addressed and a fix will be available in the upcoming STAAD.Pro CONNECT Edition V22 Update 5, scheduled to be released in September of 2020.