I'm pretty sure I don't have any other addon scenery for Basel so not sure what it could be...
Sure you have another scenery for Basel, that's from where those extra jetways are coming from. If this jetways were made with SODE, you might assume you don't have a conflict, because you removed the scenery folders, but jetways might still be there in one of the SODE folders:
C:\Programdata\12bpilot\SODE\XML
C:\Programdata\12bpilot\SODE\SDX