Location migration not working
Do not repeat the field name for sub columns: Instead of e.g. field_location/field_location_lat use only field_location/lat, in the process:  section. 

There also is no need to manually set interal keys like entity_id or revision_id: Only set the destination plugin and the field values, and Migrate module will fill all other internal columns for you.

destination:
  plugin: entity:node

process:
  title: title
  type:
    plugin: default_value
    value: NODE_BUNDLE_NAME
  langcode:
    plugin: default_value
    value: 'en'
  field_location/lat: latitude
  field_location/lng: longitude