Windows Closing and Crashing When Editing Sub-Brushes in Affinity Photo V2

[Hollyer97]

When double clicking sub-brushes on the brush editor, the sub-brush editor window opens but when I attempt to alter any characteristics, the window disappears. After a few times repeating this, the whole program crashes. 

[Dan C]

Hi Hollyer97,

Could you please post a crash report by following this guide?

Lee