I'd like to suggest that you're attempting to delve too far into psychology for what you truly understand just from your own description. I can offer an alternative explanation for observing this behavior that contradicts any of the ones you deemed related:
Users reported performance problems when told we were running on backups because performance was the only thing they weren't sure was working correctly. It was easier for users to report this issue than to test for it accurately.
Rather than pass judgements about why they did this consider a term and wording that sticks to what you know:
Informing our users that we were temporarily running on disaster recovery servers biased them to report performance issues.
This way you've only reported what you've observed.
prejudice in favor of or against one thing, person, or group compared with another, usually in a way considered to be unfair.
"there was evidence of bias against foreign applicants"
synonyms: prejudice, partiality, partisanship, favoritism, unfairness, one-sidedness; bigotry, intolerance, discrimination, leaning, tendency, inclination, predilection, casteism
"he accused the media of bias"
in some sports, such as lawn bowling, the irregular shape given to a ball.
cause to feel or show inclination or prejudice for or against someone or something.
"readers said the paper was biased toward the conservatives"
synonyms: prejudice, influence, color, sway, weight, predispose; distort, skew, slant
"this may have biased the result"
prejudiced, partial, partisan, one-sided, blinkered;
bigoted, intolerant, discriminatory;
distorted, warped, twisted, skewed
"a biased view of the situation"
give a bias to.
"bias the ball"