Endpoint AutoUpdate fails: "File copy failed."

Hello,

we're using Sophos UTM 9 in our office in combination with the Endpoint Protection bundled with it. Now, some days ago several (but not all!) of our PCs stopped updating itself and started throwing errors that AutoUpdate isn't able to connect to the server. I decided to un- and reinstall the client with the download link offered by the WebAdmin panel. Now I can't even really start up the Endpoint Protection itself, as it wants to download the rest of its components from AutoUpdate, but AutoUpdate continues to fail.

This is the error message I'm getting:

2018-05-25T14:13:58.088Z [ 4004] INFO  SUL-Log [I19463] Syncing product cd2a5386-f08c-42b1-8d98-40240059e361 591
2018-05-25T14:13:58.088Z [ 4004] ERROR SUL-Log [E35582] [DetailedException: File copy failed. [File: '53b5bdddfedeef5128a4390b4deea225x000.dat' ] [From: 'adapter|{adapter|{adapter|{http|http://d1.sophosupd.com/update/|}|}|}|' ] [To: 'file|C:/ProgramData/Sophos/AutoUpdate/data/warehouse|' ] ]
2018-05-25T14:13:58.088Z [ 4004] ERROR SDDSDownloader::ReportSyncFailure Failed to synchronise
2018-05-25T14:13:58.088Z [ 4004] INFO  UpdateLogic::SyncAndInstall Saving state.
2018-05-25T14:13:58.088Z [ 4004] INFO  StatePersister::Save Overwriting state file C:\ProgramData\Sophos\AutoUpdate\data\status\SophosUpdateStatus.xml
2018-05-25T14:13:58.088Z [ 4004] INFO  UpdateLogic::SyncAndInstall Skipping product install as Sync failed.
2018-05-25T14:13:59.094Z [ 4004] INFO  IPCSender::Write IPCSender::Write: Writing message: <?xml version="1.0" encoding="utf-8" ?><Config type="RMSEndUpdate"><ErrorMessage><ID>SDDSDownloadFailed</ID><StringID>107</StringID><Sender>SophosUpdate</Sender><Insert>cd2a5386-f08c-42b1-8d98-40240059e361</Insert><Insert>dci.sophosupd.com/.../ErrorMessage><ReadableMessage>ERROR:   Download of cd2a5386-f08c-42b1-8d98-40240059e361 failed from server dci.sophosupd.com/.../Config>
2018-05-25T14:13:59.094Z [ 4004] INFO  WinMain SophosUpdate has completed with the result 0.
2018-05-25T14:13:59.094Z [ 4656] INFO  IPCSender::ProcessSend IPCSender::ProcessSend: Send message: <?xml version="1.0" encoding="utf-8" ?><Config type="RMSEndUpdate"><ErrorMessage><ID>SDDSDownloadFailed</ID><StringID>107</StringID><Sender>SophosUpdate</Sender><Insert>cd2a5386-f08c-42b1-8d98-40240059e361</Insert><Insert>dci.sophosupd.com/.../ErrorMessage><ReadableMessage>ERROR:   Download of cd2a5386-f08c-42b1-8d98-40240059e361 failed from server dci.sophosupd.com/.../Config>
2018-05-25T14:13:59.094Z [ 4656] INFO  IPCSender::ProcessSend IPCSender::ProcessSend: No messages in queue, starting to wait
2018-05-25T14:14:00.111Z [ 4656] INFO  IPCSender::ProcessSend IPCSender::ProcessSend exiting
2018-05-25T14:14:00.111Z [ 4656] INFO  `anonymous-namespace'::SenderThreadFn::operator() Sender thread finished.
2018-05-25T14:14:00.111Z [ 4004] INFO  StatePersister::Save Overwriting state file C:\ProgramData\Sophos\AutoUpdate\data\status\SophosUpdateStatus.xml

Has someone a solution for this problem?