Why did my WhatsApp disconnect?
The alert names the likely cause (device removed by WhatsApp, logout from the phone, number moved); reconnect from Connections with the QR.
When a QR number drops, WASync emails the administrators and shows the cause it could establish on the connection: most often WhatsApp removed the linked device, which happens when the number was logged out from the phone, when the same number was moved to the Business API, or after WhatsApp's own enforcement on messages to many new contacts in a short time. The alert also says how many new contacts were written in the hours before the drop, which is the usual sign of the last case.
To reconnect: Connections → the number → Reconnect, scan the QR with the phone, and the conversations resume. Flows, the Open Channel line and the team's access stay attached to the connection.
To keep a QR number healthy: no bulk sends to contacts who never wrote to you, warm a new number up gradually, and keep the phone online. For higher volumes or campaigns, use a Business API number.