The VMD run the adverse event reporting scheme and the form can be found here.

This form asks for some data, chip number, details of migrations, chips should be reported as migrations rather than failures when the animal hasn't been radiographed to show that there is actually a microchip present. Experience suggests that some fall out through operator errors, or may be groomed out by attentive mothers. Animals should be thoroughly scanned before deciding that a chip isn't present.

Migrations whilst annoying are common and usually due to incorrect chip placement.