The root cause was a scheduled task in our infrastructure getting stuck on Friday evening 8th May. This resulted in no invoices being delivered from AutoInvoice to Visma Net ERP.
Monday morning 11th May we started receiving information about this, and after a short investigation we could identify the problem and solve it by manually restarting the scheduler task.
To prevent this from happening in the future we have now changed the configuration to automatically restart if getting stuck. In addition we will create alerts to notify this proactively.