Does pressing F5 also fix the problem? There is a bug with the auto-update logic in 0.6.0019. I already fixed it but it won't be available until the next public release, 2~3 weeks away.
I have had similar problems... and there is no assured solution that always works. Sometimes its F5, sometimes copying and pasting the affected node works, and sometimes just replacing it with another one from the toolbar. With a VB node, sometimes I have had to create another empty node, redo all the inputs/outputs and then paste the entire code from the original to get it to work.
The image parsing component's behavior is even more peculiar. I always try to keep image locations relative to the filepath of the main file, but obviously when they change computers, the absolute path cannot remain the same. If GH doesn't find the image, it doesn't give any warnings, but simply removes the image parsing component, and snaps all outgoing connections to the top left corner of the canvas. This can get very messy if the output is connected to several places... it takes a while to figure out what goes where. I think a reliable 'make path relative' will be quite handy. Or perhaps a warning saying 'image not found' instead of the node disappearing.