Step to reproduce:

• Add new widget with matomo with dimension as "All Channels" and metric as "Conversion Rate"
• Choose another dimension "Audio Resource URLs"
• Do not change metric combobox
• Add chart to dashboard
• Open edit and see metric combox is empty
• See  

See the problem:  metric combobox is empty when editing and jsonpath has been wrong as well

AC: Keep the current metric if metric is existing with dimenion or make it empty if metric does not exist

 Another case have to check after investigating is make sure in 6.2.2 when edit widget of matomo, change metric combobox, the preview field can work correctly