DIAGNOSIS This is usually your device being stubborn, not the Deco system. Phones and laptops sometimes 'cling' to the first WiFi signal they connected to, even if a stronger one is available.
FIX The Deco system has a feature to help with this. 1) Open the Deco app and tap on the 'More' icon (three dots). 2) Go to 'Advanced' and then 'Wireless Roaming'. 3) Make sure 'Fast Roaming' (802.11r) is turned ON. This helps devices switch faster. 4) Also, ensure 'Beamforming' is enabled (it usually is by default). This focuses the signal toward your devices. After turning these on, the fix is on your phone: temporarily turn its WiFi off and back on. This forces it to scan and grab the strongest Deco signal.
IF THAT DIDN'T WORK Some older devices just have bad roaming logic. You can create a separate network name (SSID) for the 2.4GHz and 5GHz bands in the Deco app's Advanced Wireless settings. Connect your problem device only to the 5GHz network. Since 5GHz doesn't travel as far, the device will be forced to drop the signal and reconnect as you move, which often solves the 'clingy' behavior.
HEADS UP Be patient after enabling Fast Roaming. It doesn't work magic instantly. It just gives your device a better nudge. The real test is moving around and then toggling your device's WiFi if it gets stuck again.