2nd stage detaches soon after liftoff

[NJK-25]

I launched  rockets with proper COM and TWR, and with aerodynamic surfaces, I am new to the game and just started making larger rockets to reach Minimus, but at about 3500m~5000m, the upper stage decouples without input(even though my stage sequence is proper) and flips the rocket ,i used the correct decoupler, with SAS engaged. yet this continues for all of the larger rockets. What is wrong here? Everything was proper for smaller rockets....

Edited January 20, 2022 by NJK-25

[jimmymcgoochie]

Screenshots please! Or even better, a video.

Are you sure you’re not firing the second stage engine too early? Is the rocket bending before it breaks? What’s your TWR at the point where it breaks?

[king of nowhere]

How is the rocket made? is there a weak joint between first and second stage? Some part that's attached poorly and can get broken easily? Maybe an engine exhaust hitting the rocket and causing a portion to overheat and explode?

Edited January 20, 2022 by king of nowhere

[Vanamonde]

Are you pulling so many Gs that the thing is suffering structural failure? Pics of the craft might help, and also try to get a shot of the F3 report right after the failure, to see what is breaking first.