The PM 75 will "see" the 14.6+ that the batteries have reached and drop to 13.6. Now it will not supply any amps because the batteries are at a higher voltage than it is. So the other charger keeps on charging by itself according to its own charging profile.
While both are running at first with 43 and 40 amps 83 total , that means the batts will only accept 83 amps at that voltage and SOC. If the batts were at a lower SOC the 75 would be at 75 and the other at 40. Total 115. The lower voltage charger will taper its amps first as battery acceptance drops below 115a with rising SOC
Look at my ugly graph for the PM100 for what that looks like. Pick along the tapering part of the curve for the Vecs or mod-PM100 to see what the SOC would be approx at 83a. That is where you were when you were seeing that 43 and 40. The only reason you saw the 43 at all was because the PM does that 15 min at 14.6 no matter what the battery SOC
All normal, no problem.
