Use created record in synchronous workflow

I have a workflow that runs when a custom membership record is updated.

The workflow creates a (custom) invoice record then places that record in a lookup on the membership record.

This works fine when the workflow runs asynchronously but when I run the workflow synchronously I get an error on the step that updates the membership record (after the create invoice step).

Here is the trace log:

Starting sync workflow 'Membership - Generate Invoice', Id: d3c3b41f-00be-e511-80da-6c3be5beefc0
Entering ConditionStep1_step:
Entering CreateStep3_step:
Entering UpdateStep24_step:
Sync workflow 'Membership - Generate Invoice' terminated with error 'The given key was not present in the dictionary.'

Is there any way to get this working synchronously?