Why does Passolo 2018 freeze when updating string lists?

I open an existing Passolo project.

Some source files were changed, so the string lists need updating.

I select the appropriate source string lists, then right-click and select "Create/Update String List".

The string lists appear to update but the status bar in the dialog stops and Passolo freezes. I have to kill the process in Task Manager.

What is also puzzling is that this same problem occurs in old projects as well, when it did not before.

Has anyone experienced this before or have an idea what might be causing this. 

Many thanks.

Will Cass