It says this in the log for all the jetways: ‘UNDEFINED.MDL’ does NOT exist!
Yes, those are the corresponding log entries when SODE displays red X‘s. Because the necessary jetway model file is not found on your filesystem, SODE will display those red X‘s as an indicator of that problem.
Installing the model files is the task of the airport installer. Sometimes, the airport developer only install those files when you enable some option in their configuration tools/managers. I think Oslo is one of those special cases, where the object model files are installed differently, all managed by their own configurator.
But again, you are better helped in the aerosoft forum. They are the publisher of that airport and they know their configurator tools for sure.
EDIT: e.g., see this thread https://forum.aerosoft.com/index.php?/topic/137757-no-sode-jetways-engm/