I guess that error “+CME ERROR: 843” will be received whenever a read/write operation is performed
on an aborted TCP client or TCP server.
In your case when you are able to ping to the server,seems strange .
I think we have an option “AT_WIP_NET_OPT_AUTO_SWITCH” which switches WCPU automatically to AT mode when the peer is closed. Using this option with “AT+WIPCFG” command will avoid the error “+CME ERROR: 843”.
Hope this of some help to you.