Console log flooded with "VMware Fusion Start Menu ... : assertion failed: ..."
After multiple attempts to solve this, I finally found the solution in a side note of a VMWare community thread:

Start Fusion, select one of your VMs (no matter which one) and change the virtual machine settings like this:
Virtual machine -> Settings -> Application Menu -> "Show only when machine is running"

After I did this the messages stopped immediately. I could even switch back to the default setting of "Always" and the messages did not reappear.