magic keyboard

5K 27" iMac - on OS version 10.13.3. Magic Keyboard. From the first week I bought them a little over a year ago, the keyboard periodically malfunctions, i.e. volume and brightness controls repeat if pressed only once but the worse problem is the keyboard types diacritics! I took the iMAC and keyboard to my local Apple Store where they reinstalled the original OS. Didn't solve the problem for long. When it happens, I have to connect via fire wire or reboot the iMAC and maybe turn off and back on the keyboard. Sometimes I have to repair the keyboard.

I have tried resetting the blue tooth connections and anything else I can find online. Nothing has solved this issue. I cannot find any reference to the exact problem of diacritics. Any help would be much appreciated as this is very annoying.