Modified By System Dynamic CRM 2015

I am using Dynamic CRM 2015 On-Premises and currently facing an issue related to Modified By field of account. The issue is that whenever someone modifies or assign the account to another user, the Modified By field of the account shows "System".It should be showing the name of the person who modifies the account. I have also checked the registered plugins,there is no code written that is responsible for this kind of functionality.
Any kind of help/suggestion will appreciated.

Hi,

you should also check the Prozesses in dynamics crm