Isn't that mostly because the Scottish feel Labour didn't represent them after Blair and they now feel like Corbyn is too left wing?
I think the faculty they stood arm-in-arm with the Tories in the indyref#1 equivalent of project fear. I think most Labour voters switched to SNP, and from the people I know that was definitely something that happened.
You have to remember at the time people were told the only way Scotland would remain within the EU was through retaining membership of the UK. I don't think Brexit was even talked about back then let alone it being a considered possibility.