VC4 500mm Layer shift on tall prints

motion

Having some problems with the VC4, this is a new build. It prints perfectly when things are up to 200-250mm high but typically on long 1.5 days or longer prints we are getting layer shifts on X and slightly on Y.

originally i thought it was hitting something while printing, which we added some more zhop for it but it made no change.

heres the latest print