Hello,
Are you trying to connect flange to equip nozzle ? Are you referencing equipment model to piping module or using both modules on same dwg?
Could you try to create new test project, create new equipment add to it some nozzles and try to connect flange to any nozzles, in order to check if this is project specific. As well, create new model in existing project and try to connect flange new equipment's nozzle to check if this this drawing specific.
As well just in case, please make sure that the relationships (Line Number, Unit, Service....) values are set in component preferences dialog.