Undefined offset: 11 in vendor/magento/data-migration-tool/src/Migration/Step/Eav/Data.php on line 651

### Preconditions
1. Magento 1.9.3.8, Magento 2.3.5-p1
2. PHP 7.3.8, MySQL 5.7

### Steps to reproduce
1. run migrate:data -a [config.xml]

### Actual result
$ php bin/magento migrate:data -a [ABS PATH]/app/code/Vendor/Migration/etc/opensource-to-opensource/1.9.3.8/config.xml

[2020-06-12 04:56:31][INFO][mode: data][stage: integrity check][step: Data Integrity Step]: started
[2020-06-12 04:56:31][INFO][mode: data][stage: integrity check][step: EAV Step]: started
100% [============================] Remaining Time: < 1 sec
[2020-06-12 04:56:31][INFO][mode: data][stage: integrity check][step: Customer Attributes Step]: started
100% [============================] Remaining Time: < 1 sec
[2020-06-12 04:56:31][WARNING]: Source fields are not mapped. Document: customer_entity. Fields: mp_cc_is_approved
[2020-06-12 04:56:31][INFO][mode: data][stage: integrity check][step: Map Step]: started
100% [============================] Remaining Time: < 1 sec
[2020-06-12 04:56:34][WARNING]: Source documents are not mapped: ajaxzoom360,ajaxzoom360set,ajaxzoomproducts,amasty_ampreorder_order_item_preorder,amasty_ampreorder_order_preorder,amasty_orderstatus_status,amasty_orderstatus_status_template,amasty_stockstatus_history,amasty_stockstatus_quantityranges,sashas_callforprice_product,tm_core_module
[2020-06-12 04:56:34][WARNING]: Source fields are not mapped. Document: sales_flat_order_item. Fields: backorder_estimate
[2020-06-12 04:56:34][INFO][mode: data][stage: integrity check][step: ConfigurablePrices step]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: integrity check][step: Url Rewrite Step]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: integrity check][step: Log Step]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: integrity check][step: Ratings Step]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: integrity check][step: OrderGrids Step]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: integrity check][step: Tier Price Step]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: integrity check][step: SalesIncrement Step]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: integrity check][step: Inventory Step]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: setup triggers][step: Stage]: started
[2020-06-12 04:56:34][INFO][mode: data][stage: data migration][step: EAV Step]: started
100% [============================] Remaining Time: < 1 sec
In ErrorHandler.php line 61:

Notice: Undefined offset: 11 in [ABS PATH]/vendor/magento/data-migration-tool/src/Migration/Step/Eav/Data.php on line 651

migrate:data [-r|--reset] [-a|--auto] [--]

*** If the EAV step is skipped, the migration actually worked sans all the attribute data.

Start with vendor/magento/data-migration-tool/src/Migration/Step/Eav/Data.php around line 651 and reproduce the failure with the reported migrate:data command and config.xml. Trace the EAV data migration for the affected attributes, then verify that the command completes without the undefined offset and that attribute data is migrated without skipping the EAV step.

Written by the indexing model from the issue text.