Apprehension of bias is a review ground, even without actual bias
You don’t have to be biased. You just have to look like you might be.
The MPC’s tips-and-traps guidance for agencies sets out the three limbs of procedural fairness: a fair hearing, a decision-maker free of actual bias and reasonable apprehension of bias, and findings based on evidence rather than arbitrariness or irrationality.
The second limb is where panels trip up. A panel member does not need to actually be biased for the process to fail, a reasonable observer needs only to be able to form the apprehension that bias might be present. Previous working relationships, shared social networks, public statements about the role or candidate, or visible friendliness during interview can all create that apprehension.
The mitigation is visibility. Declare the relationship, record how it was assessed, and document the reasoning for proceeding, or recusing.