NC Docker: Windows client not syncing - empty error message

My windows client is having sync issues and the error messages reported by the log viewer are not really helping:

[OCC::AbstractNetworkJob::start     OCC::LsColJob created for "http://nc.x.nl" + "/x" "OCC::DiscoverySingleDirectoryJob"
[OCC::WebFlowCredentials::slotFinished  request finished
[OCC::AbstractNetworkJob::slotFinished  Redirecting "PROPFIND" QUrl("http://nc.x.nl/remote.php/dav/files/Pim/x") QUrl("https://nc.x.nl/remote.php/dav/files/Pim/x")
[OCC::AccessManager::createRequest  6 "PROPFIND" "https://nc.x.nl/remote.php/dav/files/Pim/x" has X-Request-ID "50a3ff83-28c0-4c2a-b602-c9bbd8fee32c"
[OCC::WebFlowCredentials::slotFinished  request finished
[OCC::AbstractNetworkJob::slotFinished  QNetworkReply::ProtocolInvalidOperationError "Error transferring https://nc.x.nl/remote.php/dav/files/Pim/x- server replied: " QVariant(int, 400)
[OCC::WebFlowCredentials::stillValid    QNetworkReply::ProtocolInvalidOperationError
[OCC::WebFlowCredentials::stillValid    "Error transferring https://nc.x.nl/remote.php/dav/files/Pim/x- server replied: "
[OCC::LsColJob::finished    LSCOL of QUrl("https://nc.x.nl/remote.php/dav/files/Pim/x") FINISHED WITH STATUS "ProtocolInvalidOperationError Error transferring https://nc.x.nl/remote.php/dav/files/Pim/x- server replied: "
[OCC::DiscoverySingleDirectoryJob::lsJobFinishedWithErrorSlot   LSCOL job error "Error transferring https://nc.x.nl/remote.php/dav/files/Pim/x- server replied: " 400 QNetworkReply::ProtocolInvalidOperationError
[csync_ftw  opendir failed for x- errno 22
[OCC::SyncEngine::handleSyncError   ERROR during  csync_update :  "Er trad een fout op bij het openen van een map Error transferring https://nc.x.nl/remote.php/dav/files/Pim/x- server replied: "
[OCC::ActivityWidget::addError  Item  "Nextcloud"  retrieved resulted in  "Er trad een fout op bij het openen van een map Error transferring https://nc.x.nl/remote.php/dav/files/Pim/x- server replied: "
[OCC::ActivityListModel::addErrorToActivityList     Error successfully added to the notification list:  "Er trad een fout op bij het openen van een map Error transferring https://nc.x.nl/remote.php/dav/files/Pim/x- server replied: "
[OCC::SyncJournalDb::close  Closing DB "C:/Users/Pim/Nextcloud/._sync_50394354039d.db"
[OCC::SyncEngine::finalize  CSync run took  808 ms
[OCC::Folder::slotSyncFinished  Client version 2.6.2stable-Win64 (build 20191224)  Qt 5.12.5  SSL  OpenSSL 1.1.1d  10 Sep 2019
[OCC::Folder::slotSyncFinished  SyncEngine finished with ERROR
[OCC::Folder::showSyncResultPopup   Folder sync result:  2
[OCC::Folder::slotSyncFinished  the last 3 syncs failed
[OCC::ownCloudGui::slotSyncStateChange  Sync state changed for folder  "http://nc.x.nl/remote.php/dav/files/Pim/" :  "Error"
[OCC::FolderMan::slotFolderSyncFinished     <========== Sync finished for folder [Nextcloud] of account [Pim@nc.x.nl] with remote [http://nc.x.nl/remote.php/dav/files/Pim/]
[OCC::AbstractNetworkJob::slotTimeout   Network job timeout QUrl("ocs/v2.php/core/navigation/apps")

[OCC::DiscoverySingleDirectoryJob::lsJobFinishedWithErrorSlot LSCOL job error "Error transferring https://nc.x.nl/remote.php/dav/files/Pim/x- server replied: " 400 QNetworkReply::ProtocolInvalidOperationError

I’m running NC 18.0 in a docker container, traffic to NC is being proxied through by Traefik v2.0. What am I missing?

Still looking for some advice rgarding to this matter.