Enphase IQ7+ minimum Vmp is 27V,
when one sub-group is shaded, the voltage become 2/3 x 33 = 22V.
so, IQ7+ can not track the maximum point, it is why IQ7+ can not handle correctly
First, I do not know, it has been caused by an Inverter or a Panel,
but, I am suspecting that the problem is happening by The Inverter.
Because I have verified with MPPT charger with same panel, and similar condition,
and, the power generating is +1/3 and shade two cells, and +2/3 when shade one cell.
Everybody know the shadow can reduce the power from Solar Panel,
there are 3~4 strings in a panel, if shading a string, the other strings can operated normally.
What will happen there is very small shadow 1-2 cells in a 60 cells panel ?
Yes, it can reduce the production to 30~60%,
Look at the detail production yield at my house,
Sunlight is coming from Right-Top side and, Dommer at Right Hand Side is making a shadow on Panel #6,
#1, at 09:19AM, half of two cells (right-top side, two cells in horisontal, not a panel) are shade, power production is just 10% via the other panel.
#2, at 10:23AM, very thin shade on a cell of panel (around 10~20% on right-top side of cell, not panel), production is 80% via the other panel.
#3, at 10:29AM, no shades, same power gain via the other panel.
In the solar panel test with MPPT charger, the minimum power is aroudn 60% in #1, 90% in #2
It makes me suspect There is a critical problem in Enphase IQ inverter.
Note. Enphase IQ 7+, LG350N1C-V5