I have read from other historians that the claim was made up, forget where though. R and S were no different than the other stunningly incompetent Russians generals of WW1, so their failure to do their jobs right is just par for the course and didn't require anything other than incompetence.
So you do not have any sources claiming that there was no feud between the two?
In this case I think I continue to believe the story that there was a feud. Because in the meantime I have been reading about the politics of the Russian army (trying to find an non-hoffmanian source for the feud), and while I could not find other sources for this I did find others describing the disputes albeit not due to a personal feud but in the context of the politics of the Russian army. Rennenkampf was a friend of grand duke Nikolas while Samsonov was a protégé of the war minister Sukhomlinov. The latter tried to modernise the army, and the former tried to sabotage and undermine him at every turn. For instance the duke got the Tsar to cancel war games that were planed by the War minister. Nikolas and Sukhomlinov both had their loyalists which were feuding.
This would be disastrous during when war broke out as both fractions had to be given equal representation, e.g. the two armies in east Prussia got Rennnenkampf (as a partisan of the Duke) and Samsonov (as a supporter of the war minister).
So even if the incident described by Hoffman did not happen there are other reports of a feud between Rennenkampf and Samsonov.