This looks to have fixed it. Thanks for your help Anton.
UPDATE: Noticed that it only seems to happen when resizing the Rectangle that is being shared. So does not appear to be related to scrolling (I am resizing the window if the coordinates become out of bounds against the parent, as soon as that happens it crashes). It also happens by just maximizing and restoring as the browser size (and rectangle that is shared) is responsive Using the tvnviewer.exe I can see the following error: Error in TightVNC Viewer: Error in protocol: incorrect size of rect...
UPDATE: Noticed that it only seems to happen when resizing the Rectangle that is being shared. So does not appear to be related to scrolling (I am resizing the window if the coordinates become out of bounds against the parent, as soon as that happens it crashes). It also happens by just maximizing and minimizing as the browser size (and rectangle that is shared) is responsive
Server crashes after too many updates