Stickup Cam not charging from solar panel

Back in September I bought a Stick Up Cam and small solar panel. While the solar icon is there in the camera settings, it has never charged off the panel. Periodically I have to pull the battery out and charge it directly with a USB cable, which works fine. My understanding is that it won't charge from the panel if the battery charge is already high enough, but it goes down below 50% and still won't charge. I have a USB power meter which shows that the panel puts out just under 5v. I have tried replacing the panel with a USB powerbank and the camera won't charge from it, either.