Mouse Inputs don't seem to be detected after Upgrading to 2019

After upgrading to 2019.3 from 2018 my game does not work properly ...mouse clicks don't seem to respond well...as if it does not register inputs such as on mouse down, mouse drag and mouse up...
WHAT SHOULD HAPPEN:
my game is a city builder and the way building a city should work is you click on button to place a building then on mouse down onto a grid will start spawning preview prefab as we drag mouse diagonally ... as we keep dragging system will keep placing more prefabs... on mouse up system stops adding new preview prefabs and replace those preview ones with actual final prefabs ...

WHAT ACTUALLY HAPPENS:
But when I Click on a grid and start dragging input On Mouse down does not seem to be registered, and preview prefab is not being spawned... yet if I was now to click on different location system behaves as if this is the final 2nd input and tries to place preview prefabs ...as if I was dragging mouse to that point ...then when I let go of the mouse .... preview should have been replaced with actual prefab ... yet preview prefabs are still there even though I did release mouse button and as if on mouse Up has not been detected ....

then if I click anywhere again, this 2nd on mouse UP seem to activate the final stage of replacing preview with final prefab ....
everything is a mess

I must say this all worked great in unity 2018 ... but after upgrading this all got messed up

So why was I upgrading then... my game use terrain holes which can only be used from 2019.3

If you have any idea why is this happening, what could be causing it and specifically why after upgrading to 2019 my inputs goes all crazy please please let me know... it has been a month I have been trying to figure this out ...and I am literally going crazy! THANK YOU SO MUCH IN ADVANCE!

 

Unity changed their input system in 2019. Maybe your settings got lost or messed up. Check
ProjectSettings\InputManager.asset

Also:
https://docs.unity3d.com/Manual/class-InputManager.html

 

Thank you after a month of stress and headache I finally realized what happened, I had my prefab placement preview in fixed update ( because I needed physics) with the inputs, But 2019 has improved performance of the engine so much ... that fixed update now lags visibly for my purpose and does not pick my inputs anymore in real time... I had to move all inputs into the update , whilst leaving the physics part inside fixed update ...