To identify such addons I normally do this:
Use an addons profile addon like "Addon Selector".
Save the current active addons to a profile.
Disable half of the enabled addons (upper half) by clicking on 1st addon and then scroll down and SHIFT click on the addon at the middle of the list.
ReloadUI and test if the changes are still visible or not.
If not: You disabled the addon in question most probably.
Load the saved profile at the addon manager again, disable the lower half now and enable the upper.
Is the change visible again now? You are sure it's in the upper half.
Go on enabling/disabling half of the addons (e.g. disable the half of the upper half, then the half of the half of the upper half, ...) until you find the addon in question.
It's good to narrow it down without having to test each single addon.
If you know how to find out the name of a control below the mouse cursor you can use that too to find the control name of the addon in question.
e.g. move the mouse above that FPS meter where the 152/215 is shown.
Type into chat:
Code:
/script d(moc():GetName())
It wil show you a name of the control below the mouse, e.g. something like ZO_FPSMeterLabel1
Search for that name or parts of the name like ZO_FPSMeter withn your live/AddOns folder.
The free text editor Notepad++ provides an easy way to do this, via the menu File->Search->Search in files & folders
Just search all *.lua and *.xml files and you will find the addon names where this control is used/changed.
So you can disable those to see if this could be the addon in question.