Why doesn't High Serria 10.13.3 respond to blue tooth mouse and keyboard

I have 2010 iMAC 27 desktop with High Serria 10.13.3. It still works great. However, lately, the system suddenly stops responding to my wireless mouse and keyboard. I reboot 4-5 times but does not respond to wireless devices.

I hit Option + Command + R and reinstalled the lastest OS, which takes about an hour to download and install.

The system reboots and my wireless devices once again work find. This problem is starting to re-accure more frequently.

Any ideas on how to fix without buying a new computer?

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