Why does the client sometimes not update the data?

Background Processing vs. Minimising

You can continue working in other programmes during the Data Transfer.

Caution when Minimising 

Please note that minimising the client causes the Data Transfer to be Interrupted and will only be reactivated when you activate the client again. 

Data Transfer in the Background

If you want the Data Transfer to continue in the background, then leave the client Open and bring another programme to the Foreground.