If it is an agenda in a new team, the agenda has most likely been transferred to FirstAgenda, but you have not added yourself to the new team yet. Read about how you join a new team.
the upload-client has stopped
You can also check if the agenda has been transferred to FirstAgenda in the first place. You can check when the upload client was last running here: How can I see the latest server connection to the upload client?
Take contact to the responsible IT manager in your organisation and make them check if the source directory, where files are transferred from, is empty. If the files are in the source directory, it might be that the scheduled task that runs the upload client has stopped. Your IT manager will need to get this running again.
If the upload client source folder is empty, it may be due to an error while importing. Check out the page “Show failed imports” and see if your agenda is here.
Read about how to fix this error here: Why has my agenda failed?
If you have looked at and tried all of the above without success, contact FirstAgenda Support at firstname.lastname@example.org for further investigation.