Oh yeah, bit of shade will do it for sure.
What percentage of a single cell has shade? 90%, so only 10% of one cell is getting sun? If so, current from that cell is only 10%, and current from entire panel and string is only 10%.
With sufficiently long series string, it is possible for the other panels (or diode-bypassed portions of this panel) to push their current past the partially shaded diode-bypassed portion. But if there is some light on each cell of the partially shaded portion, MPPT controller may stop at a higher voltage power peak with that 10% of current, and miss a lower voltage peak (75% of voltage) with 100% of current.
Various shading situations aren't always handled well by charge controllers.
You need to see how your array performs in full sun, no partial shading.