How to prevent reloading of a form

I am using a mscrm 365 on - premise UCI.

On my onload event I have an alert that pops up once in 2016 version, but now in 365 UCI it pops twice, I checked it in F12 and I see the onload fires twice for no reason, how do I solve that? and make the onload triggers once, I checked form properties is declare there only once.