I will start below steps :
1. I will start with the Config. is there any change in WLC config when we move from 8.8 to 8.10
2. re-visit the release notes and look for any ISE compatibility issues :
https://www.cisco.com/c/en/us/td/docs/wireless/controller/release/notes/crn810mr2.html
3. Login to WLC and debug the logs and see what is wrong.
4. Visit ISE debug logs and see any abnormal logs or is the request reaching ISE.