Thank you @borate
I already have the pdf help file on my PC. I have just reperformed the following searches "disable", "grid", "animation" and "animation grid", which I did before opening this post. I have also reread the effect masking section. I found no mention that a snap to grid exists nor how to turn it off, and as an aside no mention that it is critically important not to add or delete node points when using the effects animation editor.
Please do not think that I am completely dissatisfied with VP, I am not. It does all and more than I could want at the moment, and the help I have received through this forum and directly from VP technicians has been the best.
Regards Dave