Yesterday, June 3rd, we posted this incident on Visma WebInvoice / Visma Webfaktura by mistake, it should have been posted as an incident on Visma Webbfakturering SE.
This issue, affecting Visma Webbfakturering SE and not Visma WebInvoice / Visma Webfaktura was solved by restarting an instance of an internal component called messagestore.