If the results can be polluted by other non-gravitational effects, then they can also be created by non-gravitational effects.
Evidence, please, that the second half of that sentence follows from the first. Quote me a physicist (because you're just a random internet person, you see) who actually say that the existence of an error source in an experiment could mean that the totality of the result is in fact something other than that which they thought was being measured.
They just don't know what they are measuring, as stated by Quinn above.
Where does Quinn say he doesn't know what they are measuring? He certainly says, as do his colleagues, that they can't account for all of the errors, but there is no doubt in any of their extensive work that they doubt the existence of G. The wildest assertions anybody is making outside of this forum is that G might in some way be slightly variable, but even that is generally viewed as a fairly wild opinion.
Since you only listen to physicists (apart from when they describe the shape of the earth or the existence of gravity), here's our man Quinn introducing the very Royal Society event that you have bizarrely used to imply that G doesn't exist:
A misunderstanding of the metrology of weak force physics may in turn imply that the experimental tests that have established the inverse square law and the universality of free fall thus far are flawed in some subtle fashion. This makes for a potentially exciting situation and perhaps explains the general interest shown in our apparently mundane and painstaking work on G.
It's great read - lots of detail from Quinn, and numerous papers outlining many fascinating ways of measuring G. No mention of anybody believing that G doesn't exist, or that the earth might be flat, but to fair I didn't read them all. Do let us know if you find any juicy quotes Tom.
https://royalsocietypublishing.org/doi/10.1098/rsta.2014.0253?cookieSet=1