It would seem that PrecisionEngineering has some problems in combination with Traffic Manager in an odd way:
Consequences of this bug, is that the fps drops significantly over time in the main menu when this is happening (perhaps because of all that loading?). Another thing to add, is that when this is happening, and you happen to open a window in the main menu (e.g. new game, tools, content manager, etc.) and try to close that, it throws the following exception without allowing me to close the window:
NullReferenceException
at (wrapper managed-to-native) UnityEngine.Behaviour.get_enabled () <0x00075>
at ColossalFramework.UI.UIComponent.get_isEnabled () <0x0001c>
at ColossalFramework.UI.UIComponent.Focus () <0x0005a>
at ColossalFramework.UI.UIView.PopModal (int) <0x001aa>
at ColossalFramework.UI.UIDynamicPanels.Hide (string,int) <0x000f3>
at LoadSavePanelBase`1.OnClosed () <0x0006e>
at (wrapper dynamic-method) object.DynamicEventWrapper_OnClosed (NewGamePanel,ColossalFramework.UI.UIComponent,ColossalFramework.UI.UIMouseEventParameter) <0x00018>
at ColossalFramework.UI.UIComponent.OnClick (ColossalFramework.UI.UIMouseEventParameter) <0x000c8>
at ColossalFramework.UI.UIButton.OnClick (ColossalFramework.UI.UIMouseEventParameter) <0x0027f>
at ColossalFramework.UI.UIInput/MouseHandler.ProcessInput (ColossalFramework.UI.IInputTranslator,UnityEngine.Ray,ColossalFramework.UI.UIComponent,bool) <0x00bd1>
at ColossalFramework.UI.UIInput.ProcessMouseInput () <0x002ba>
at ColossalFramework.UI.UIInput.Update () <0x00055>
(Filename: Line: -1)
Trying to close it the second time seems to work though and prevents the exception from happening again.
I hope you can replicate the issue. I've nailed it down to Precision Engineering and Traffic Manager. Without Traffic Manager, Precision Engineering works fine.