As explained in other threads, there are still bugs in Jetways in SU5, even after 2 hotfixes, since none of them addresses jetways.
Asobo has confirmed there have been some undocumented changes in how jetways works in SU5, so they promised an updated SDK and documentation, but without providing with an ETA, because the problem of jetways randomly disappearing affects even default airports using default jetways and, in fact, when asked about that, Asobo replied they first need to fix the jetway system, before they will document the changes.