Hi all, and thanks for your input.
I actually solved this yesterday and tried to update here, but could not post as limited to one post per day! So sorry about that.
For reference, the issue was 2-fold:
1. It doesn't seem to like nested symbols. My 'House-Type' is a symbol, which contains a 'label' symbol to which the record is attached.
2. The symbol seems to need some geometry. My 'label' symbol only contained text.
Solution:
I added an invisible polygon to the 'label' symbol. This solves '2'
I then set my 'House-Type' symbols to 'convert to group' when placed. This solves '1'.