Uploaded builds don't appear in Testflight

Hello, new developer here, trying to get a build on Testflight. I’ve archived and uploaded a number of builds via Xcode, but none of them seem to be appearing under the Testflight tab in iTunes connect - they don't even show up as 'processing'. The builds have the correct bundle ID, and I know they’re uploading successfully since when I try to re-upload one from my Archives list I get the following error message. Has anyone else had this problem?