Monitor resolution problem

Hoping someone has ran across this problem before... We have a user who's monitors change resolution when booting up his computer - sometimes. 

 He has a Dell T3610 with Windows 7 pro. and 2 Dell P24H17 monitors. When booting up his machine the main monitor is supposed to be on the left.  They are both hooked up using Display port cables.

Now the problem: It took 3 or 4 times of restarting his machine, before the problem presented itself.  But on boot up the login screen changed monitors and then once logged in, the resolution on the monitor on the left was turned way down. The monitor on the right was still as it should have been but was now the main screen. 

 I then checked the graphics driver which was up to date, next the monitor drivers - those did need updating (they were showing "generic pnp") but now showed correctly after updating  ("dell model#" and connected with "display port".) after a day or two he comes back to say the issue is still persisting. Now the left hand monitor driver seems to have reverted back to "generic pnp" and when I try to update the driver it doesnt do anything. The right hand monitor is still showing correctly in device manager and the resolution is fine, but switched again on its own to being the main display. I dont believe it is the cables but have not changed those out yet. Please see pictures below for reference (note I had already changed the left-hand monitor to be the main again by the time i took the pic.)

Any help with this problem would be greatly appreciated.

for pics please see the post on microsoft forums.. pictures cant be over 1MB here..  

https://answers.microsoft.com/en-us/windows/forum/windows_7-hardware/monitor-resolution-problem/28583331-5947-4aae-acdb-31d0bf8a4085