Many of the resistance members flip-flopped back and forth as new information was revealed regarding +F's treachery, followed by denials or temporarily soothing explanations. They wanted to give him the benefit of the doubt until it became patently impossible. Flip-flopping can also denote "course-correction". I can't find fault with that unless it is habitual and flippant.
Does part of Bp. Fellay's treachery involve changing his mind about the authenticity of DM's messages by any chance?
No. I was thinking more along the lines of his treachery involving trying to sell out the SSPX and the 2012 Declaration. I thought this was a resistance-supporting site? Do you support the resistance? (Meaning one concerning the SSPX, not the general one against Rome) Do you think Bishop Williamson is a good and credible bishop?