This is something the Google should check out and give answers / instructions. I have noticed the same problem and the problem is not related to the interface you are using: AI Studio, Mobile or Gemini directly in browser. When you upload file, the uploading symbol just rotates indefinitely.
There is something wrong in the upload service. Is it restricting uploads after certain amount of uploads or what? If so the Gemini should tell user about it. I wonder if acquiring the advanced version would stop this problem? This is very annoying especially if it happens due to data amount restrictions but the reason is not told to the user. These kind of big glitches with no logical reason makes usage of the engine unreliable.