Steps to reproduce this bug on demo site:
1. Log in to application
2. Open any window (sales order for instance)
3. Go to Preference>Manage Gadgets
4. Remove a gadget (Views for instance)
5. Go to home tab and you get performance gadget empty.
Reproduced, maybe the "Manage Gadgets" must be shown just if you're in Home tab?
Workaround to make the performance gadget reappears - maximize it and restore it.
Triaged by Diego Ruiz,
The issue is still present and the workaround still works in 7.1z