Character keeps jumping on uneven terrain

Hi guys,

First of all, below is the link of the video about the issue:

https://www.kapwing.com/videos/611fecb66e83390044b035f9

I created a character using capsule collider and rigidbody, and I imported a terrain from asset store. When the character moves on a cube or other flat grounds, it moves properly. However, when it tries to walk on a bumpy terrain, it can move, but repeats the motion of jumping. When I play it and look at its animator, its jumping animation turns on over and over again while walking. It sometimes walks properly on a certain area of the terrain. I checked out the "isGrounded" through using RayCast, but it was on the ground all the time except for the moment I press spacebar ("jumping"). Does anyone know how to fix this issue?