On the other hand, I tend to doubt that DC leakage itself would affect
the bridge. It is probably an AC bridge with an AC voltmeter. However,
the real part of the admittance at the operating frequency of the
bridge, might affect its ability to find a good null.
Does the HP manual give any recommendations for measuring components
that are already grounded and not floating?
Maybe you need to isolate the LCR meter from earth with a transformer.