Magento – Magento2 Data migration getting stuck at Step Customer Attribute

My error was that I did not have a source prefix defined in config.xml file.

I had to change <source_prefix /> to <source_prefix>gfit_</source_prefix>

Your errors are self explanatory. Did you read the migration documentation?

I'll try to guide you in the right direction:

As you can see, your old M1 Database contains a lot of extra tables or fields for custom modules. For example:

• ebizmarts_mailchimppro
• interaktingslider_slide
• mobicommerce
• twlogin

to mention a few.

Now, from the documentation:

Some Magento 1 entities (in most cases, coming from extensions) 
do not exist in the Magento 2 database.

This message appears because the Data Migration Tool runs internal 
tests to verify that tables and fields are consistent between 
source (Magento 1) and destination (Magento 2) databases.

So you either install the M2 versions of the modules, or you tell the migration tool to ignore all the unmapped documents or fields by editing your map.xml file. Read the documentation as to where to configure which map file is used for your magento 1 version.

Then ignore all the fields and tables, for example:

<ignore>
  <document>addtocart_device</document>
</ignore>

and

<ignore>
   <field>catalogrule.attribute_to_select</field>
</ignore>

If tables or fields are called differently in M2, you can rename tables or move fields by using eg:

<rename>
  <document>sales_flat_quote_item</document>
  <to>quote_item</to>
</rename>

and

<move>
  <field>catalog_category_entity_varchar.entity_id</field>
  <to>catalog_category_entity_varchar.row_id</to>
</move>

respectively.

--- edit as per comment:

Example error:

[2017-09-06 14:00:06][ERROR]: Source fields are not mapped. Document: sales_flat_order. Fields: onestepcheckout_customercomment,orderfromplatform

Fix:

<ignore>
   <field>sales_flat_order.onestepcheckout_customercomment</field>
</ignore>
<ignore>
   <field>sales_flat_order.orderfromplatform</field>
</ignore>