my dual monitors keep switching. How can i stop this?

within the company i work for many users require dual monitors. The dual monitors work ok. But once the computer is turned off and turned back on the dual monitors sometime switch sides. i can simply switch the monitors back but this becomes anoying after a while.

When i turn the computer on i have tried switching things on in specific orders. This still doesnt help. EG i will turn the pc on first the the left monitor and then the right monitor. The computer still changes the screens randomly. All the pcs run various windows operating systems and all use citrix to access programs etc.

Any help?