You could have a dud solar panel.
Crapple caused solar panel electronics to be modified to reset their output to encourage Crapple to charge faster.
So all devices see resets, more so the smaller ones, because the solar panel cannot know why the device isn’t taking all the energy
The more typical problem is the opposite, the solar panel doesn’t reset when using Crapple. So the problem began with Crapple and the better solar panels do a hack to seek to overcome Crapple. So ironically you may be seeing a good solar panel.
The perfect ultimate answer is everything to go to USB-PD future where any voltage and any current is used. Then the solar panel doesn’t need a regulator. So go back to basics of why USB. The cells in phones are around 4V, you lose a bit of voltage in the cable and the port, so if USB we’re 5V you are well balanced for a simple charging DC DC in the phone. Solar output voltage varies is not USB hence that hard small box inside the panel to DC DC regulate to 5V. As sun varies the voltage is kept near 5V and the current varies. Crapple sees the variable current and goes obtuse and moves to trickle charge. So the regulator evolved in solar to frequently reset as it’s current varies, a solar adaption to encourage Crapple to just be less of an idiot.
Your own review of how fast is the recharge shows the hack is working!