MultiTerm 2017 issue

I have been working smoothly with MultiTerm in conjunction with Studio 2017 for around 6 months, but today there seems to be a block in adding new terms from the Studio editing window. When I try to add a new term, a term I added earlier today appears in the MultiTerm add popup window. A message appears indicating that the new term has been added, but none of the entries since that earlier term have actually been added.

Does anyone know how I can resolve this?

Many thanks in advance, Simon