After checking with the AppManager team there were no problems with the service at the time of your report.
Similar issues can appear when the metadata of the file is not correct or corresponding to the file extension. For example, an IPA file is uploaded but the file extension is not correct, which obviously should be .ipa for iOS app packages.
That is why my suggestion would be to double check the application package and file extension you are building and uploading to AppManager.
Let me know if you have further questions.
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