Error: user does not have privilege to the process that the activity is about to start

So i have one process model that calls around 4 subprocesses .

There are two users for whom i am getting the error as mentioned in the Subject. Now there are instances that run successfully and there are like 2-3 instances that fail for not a particular subprocess call. i.e. if one fails in the first subprocess , then second instance fail is on the second subprocess with the same error.

yes the user was deactivated before and then added again using SAML. We tried removing the user from the group and re adding the user back. But still the same issue. It isnt a blocker for the user as not all instances are getting this error. But im trying to understand how the system is failing in the middle.

Thank you in advance.