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".

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".