Count of unread mail jumps

Problem

The count of unread mails is jumping between the correct (151) and another number (42).

This goes back and forth every couple of minutes.

Context

It happens regularly, although I cannot force it in any way to “jump”. It just does.
I use this account with various other clients, none of them show this behaviour.

Email Provider

Web(dot)de (quite common German mail provider)

Setup

  • OS and Version: macOS Big Sur 11.2.3 on M1
  • Installation Method: Installer
  • Mailspring Version: 1.9.1.