I have custom modules for employee to enter personal details, references of previous employment etc.
So basically HR creates a User/employee and the workflow creates a new record for personal details for the new employee and adds relation to the newly created user/employee.
It used to work fine before. Off late I have noticed that the personal details record is created around 7-8 times.
Hey,
hmmm, You mentioned that it used to work fine?
Do you know if anything major has changed on the instance that could cause this change in behaviour?
(Server Change / CRM Upgrade / Workflow has been modified / Code changes / etc…)
It might also be worth checking the "Process Audit"subpanel on the Workflow itself
How many times do you see the record in this subpanel?
There should, ideally, be one entry per run of the Workflow. (In this case, One entry per new User/Employee)
If you see it appearing many times for each new User/Employee, then we might be able to narrow it down to the Workflow being the issue
It might also be handy if you could provide a screenshot of the Workflow?
(ie; The “Basic”, “Conditions” and “Actions” sections)
We may be able to quickly identify any oddities from there! 
I’m having the same issue when trying to use drop-down field values to trigger conditional tasks/notes/assignments. One thing that I recommend looking into (and am currently looking into) is if you have another workflow potentially creating a “conflict” - I find that if I make the workflow run on “New Records” vs “modified records” then the problem doesn’t exist. Just sharing and hopefully point you in a direction to find resolutions! =)