bitcoin-cli error: couldn't connect to server on importaddress
The arguments for importaddress are:

Arguments:
1. "script"           (string, required) The hex-encoded script (or address)
2. "label"            (string, optional, default="") An optional label
3. rescan               (boolean, optional, default=true) Rescan the wallet for transactions
4. p2sh                 (boolean, optional, default=false) Add the P2SH version of the script as well  

So, you need to use ./bitcoin-cli importaddress mvcWTfVhCMhwvqQf2TKkEqpLrNdW7Uekod "" false

Also, you may consider adding a final true argument after the false.

Note that importing without rescan means your utxo's will not be found (using bad terminology, your addresses will have no balance).

Also, note that since you have so many addresses to import you may wish to consider using importmulti the usage of which is described via ./bitcoin-cli help importmulti