I have just tried to upload again a new build (just changed version number) and it went through OK. I can see it in the Activity tab and is available in TestFlight, so the issue seems to be resolved now. However, no trace of the previous upload attempts.

Same issue here. Uploaded a build OK last night from XCode but it didn't show int he Activity tab in Connect. Tried again with the same build and got the message about the same version being already in the store. Nothing has changed as of 5 min ago. We tried with another build, which went through OK from XCode, but still nothing visible in the Activity tab.