Painfully slow sync speed and crash to desktop

For the past 2 weeks or so, I've found OneClander is suddenly really slow at synchronising (to Google calendar) - making any new addition or change to an entry triggers a painfully slow sync. If I try to do anything else while that is happening (or act a normal, forgetting it's running slowly!), the app crashes to desktop.

Annoying, since it's been fine for a couple of years.
I did email support a few days ago but zero response.