Hello,
I tried to import flow with the subflow that already exists in my flow instance by selecting option "import copy", that resulted in "link in" & "link out" were not connected to anything.
As i understand this can be a problem with ID link between specified link nodes.
I think it's a node red core bug to be fixed. Can someone confirm it's a common issue?
I have to admit now when i try to recreate the problem everything is linked without an issue, but as long i know this is not first time when the links in the subflow weren't connected after importing. Can't really say what triggers the problem as it happens randomly.