Outback FM80 vs. MX60 charge controller

Lunker

Hello all,
I’m new here and this is my first post so I’ll try to keep this as brief as I can;
Been happily off-grid for 20+yrs now. Recently replaced our working Outback MX60 (60amp) charge controller with a FM80 (80amp) since our array was approaching “red line” on the 60 - getting roughly 60amps (1100ish watts).
Got the new FM80 installed and in the same full sun conditions it will only produce mid 40s amps and max (observed) of 820 watts.
After consulting Outback tech support (several times) they agreed to send a replacement. Got it yesterday and tested the new one today with the exact same results. 

To make sure I’m not comparing apples to oranges I tried the same test on both the 60 and 80. That is: After a complete bulk/absorb/float cycle I set a equalize charge at a voltage it would struggle to get to (16v). The MX60 would give its all at about 1100 watts tryst BG to reach the set point. In the exact same test, same conditions and just minutes apart, the FM80 still only puts out about 760 watts (820 is the highest I’ve seen on both the first FM80 and the one I received yesterday).

Outback tech is stumped and sent it up the chain of command so I’m hoping for a call from their engineering department on Monday.
But in the meantime, it’s making me nuts.
When they offered to send me a replacement I knew in my gut there was nothing wrong with the first one and sure enough… the second one performs exactly the same. 

I do have to give Outback a huge thumbs up for trying - they immediately sent out the replacement with a shipping label to return the other. So right now I’ve got two new FM80s and the old (18 year old!) MX60 that still works as designed.
So much for keeping this brief but any feedback/suggestions would be appreciated. My hunch is that there is something in my system it’s not liking or something in the settings that tech hasn’t thought of (I have tried reverting to “default” settings and a “soft” restart with no difference).
 I’d sure like to cover as many bases as I can before I get a precious few minutes of time from the engineering department on Monday(?) so I’m all ears…

BB.

Welcome to the forum Lunker!

One off the wall question--Do you have a battery "desulfator" on the battery bank (a device that makes "electrical pulses" that are supposed to resolve Sulfates on FLA batteries)?

Years ago, we had a person here who found a desulfator was messing with some version of Outback charge controllers (Don't remember the post details--Can look up if needed). Basically disconnected the desulfator and the (newer?) Outback started to produce the expected amount of current/power...

Any other wiring issues? Loops of wires, RF transmitter (HAM, etc.) could (possibly) interfere with an MPPT battery output.

-Bill