Hello @PriteshTandel
May I know the model & OS of iphone , and model &hardware version of RE? For 'Iphone is taking to much time to conmected to extender because of weak security.' How long iPhone will take to connect extender's Wi-Fi?
Please check if the weak security warning on IOS is the case discussed in thread below, there provides some tips
[Solution]iPhone iOS14 recognizing the range extender wireless network as "weak security"
If not, can I have a photo of the weak security warning, the model of router, and a photo of router security settings. Did you try to reset RE and set up again as suggested above. Thank you.