@Supporter Thanks for posting in our Q&A.
Honestly, I haven't met this issue. What I think of this issue is:
1.The device is older OS.
2.The device onboarded into Defender. If there is a scan policy, it will cause the high CPU.
3.Internet speeds
If there is anything update, feel free to let us know.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.