As per https://www.elmelectronics.com/help/obd/tips/#327_Commands:
If a connection is lost, you will need to tell the ELM327 to ‘close’
the current connection, with a Protocol Close command (AT PC).
This will ensure that the ELM327 starts from the beginning when
the next request is made. This is particularly important for the
ISO 9141 and ISO 14230 protocols, as they need to send a special
initiation sequence.
Once the protocol has been closed, it can be re-opened by making a
request such as 01 00 (do not send ATZ or AT SP0, as many do).