I am unable to upload any files to the assistant. When I click "upload", it shows me the "exploring <filename>" page, but there is no response or text entry field. See screenshot: 
I've tested this today on Firefox, Firefox Focus, and Chromium on Android and desktop Linux, using txt and pdf files, with both the Expert and Fast modes. All tests yielded the same result.
I tested with some files I have successfully uploaded to the assistant in the past, as well as a new very small text file with just a single paragraph pasted in.
During one test on Android, I got a server error page. Screenshot: 
To reproduce:
Normally the assistant returns a summary of the file, and presents a chat box I can type further prompts into.
