Black image appears when downloading temporary materials on WeChat

Question

Guys, I use jssdk to call the photo in the WeChat h5 page, and then upload it to the temporary interface. Pass the obtained media_id of the WeChat server back to the background through ajax, and then download the picture from the temporary material to the local. The first operation is perfect, and then it will continue. There are a few more black pictures with the words loading imag... in the middle. Can anyone tell me what's going on?