“Problematic” being the catch all term to throw out rather than make an actual claim. Was the study faulty? Was the funding clandestine or did they attempt to conceal it? Does the Gates foundation support meat reduction for ideological reasons, rather than evidence based ones? Is The Gates foundation an industry that has a vested interest in continuing that industry (like an oil company funding oil benefit studies), and if so, what “industry” is that? What would they stand to lose, or gain, from the outcome of this study? What would they stand to lose or gain from any study, when their goal seems to pretty clearly be based on using the best available evidence to inform their charity programs? Is there anything at all beyond a charity that focuses on evidence based programs funding research to help inform their programs?

It might be if the Gates Foundation had funded the study.

https://bmcmedicine.biomedcentral.com/articles/10.1186/s1291...

Wellcome Trust receives significant funding from the Bill and Melinda Gates Foundation.