I had the same issue with my device (Note 3). T-Mobile doesn't seem to have a "Connection Optimizer" feature in its line of phones. In T-mo's case the feature that needs to be disabled is the "Wi-Fi Manager". 

To disable this feature you need to do the following: 

- Access your T-Mobile account (for me I just press on the "T-Mobile My Account" App). 
- Press the menu button on your device, then select "Options". 
- Under "Notifications" uncheck the box marked "Display Wi-Fi Manager notifications". 
- Under "Connection Assistant" select "Open Wi-Fi manager". 
- Uncheck the box for "Manage Wi-Fi Connections". 

That's it... 

I talked to T-mobile tech support about an unrelated issue and offhandedly mentioned this problem. The rep informed me that this was a known issue and stated that this issue was being addressed. In the mean time disabling the "Wi-Fi Manager" is a temporary fix to address this problem. Here is the shorthand way to disable the Wi-Fi manager:

T-Mobile My Account -> Menu -> Options -> "Display Wi-Fi Manager Notifications" (Uncheck) -> "Open Wi-Fi Manager" (under "Connection Assistant") -> (Uncheck) "Manage Wi-Fi Connections".