Matching solar panel to charging controller
Your link can't be opened, but I do think it relies on CN3722, a Chinese version of BQ24650. It is a buck converter, therefore V_panel &gt; V_bat. You have to set the MPPT point with resistors according to your panel - note that this is not a true MPPT converter.
If the voltage falls bellow the V_bat voltage + voltage drop on swishing element, let's say 1.5V then it won't charge.
The panel voltage can be lower, even at the sun bright if one of the cell is shaded.