Zoom function in viewer window fails when graphed view six times

Hi there

Apologies for what might turn out to be a daft question but I am a complete and utter noob when it comes to RStudio and associated packages.

I am currently using the Diagrammer package to generate a visual using the following code (which works fine):

library(DiagrammeR)

DiagrammeR("
graph TD;
A[rect]-- add style -->A2[rect + style];
B{rhombus}---|+ some style|B2{rhombus + style};
C(rounded); D((circle));
style A2 fill:#c12,stroke-width:5px;
style B2 fill:none, stroke-dasharray:10;
")

The problem I have is viewing the resulting visual consistently via the 'Zoom' option in the 'Viewer' window. It will work for half a dozen times but after that, it generates the following error:

This site can’t be reached
The web page at http://localhost:24677/session/viewhtml6fb86feb3a25/index.html?viewer_pane=1&no&host=http%3A%2F%2F127.0.0.1%3A41872 might be temporarily down or it may have moved permanently to a new web address.
ERR_SOCKET_NOT_CONNECTED

I get the same scenario when using the 'VTree' package.

I guess it's a configuration issue but to be honest, I wouldn't know where to start so any help would be very much appreciated.

Thanks

...by the way, this does start working again (for six times) if I restart R via the 'Session' menu.