The 2-AC-source scheme to generate 3-phase supplies seems workable to some extent. At least in my own simulations the current flow operates in 3 equally staggered phases.
However I wonder about current flow through a mix of 1 transformer and 2 transformers, and whether and how their flux fields build and collapse at the proper times.
Notice that another way to derive the same scheme is to begin normally with 3 AC sources arranged as conventional 3-phase delta, and then remove 1 source (while keeping its load in place). This does not prevent proper functioning afterward. The loads correctly continue to receive power.
However, yes, this does introduce power factor error which could resemble the problem you describe. Even as I remove 1 raw generator out of 3, I observe power factor error in the two remaining generators. No reactive component is present. No inductors or capacitors.
And if 2 transformers are contributing then it must depend on the accuracy of the simulator, as to how 2 transformer create a pattern of flux fields building and collapsing (120 degrees out of phase) and power their own loads as well as a third load 120 degrees out of phase with each.