Hello Zeeshan,
I have noticed the same yesterday wrt the Z50ii and recently arrived 28-400mm lens - I setup and tested the camera for my wife yesterday, and I thought it might be the lens missing focus in 3d and Auto-area AF. Will further test tomorrow, but it might be the AF jumping around and missing focus. Tested the lens on my Z8 today, and it was fine.
I will get back to you if I find anything but might be some FW tweaks are needed to optimize the Expeed7/ AF for that ASP-C sensor. Perhaps others will chime in