Serial data transmission follows the USPS model. The USPS does not guarantee to deliver the mail on time. They guarantee to try.
Serial data does get lost/corrupted. Your sender and receiver need to implement some sort of protocol to deal with that fact. Send something like <5:1ISED>, instead of 1ISED. 5 is the number of characters in the packet, < and > are end of packet markers, and : is a separator.
If a < or > is lost, that fact is easy to determine (<5:1ISED<5:2ISED><5:3ISED> is missing a <; <5:1ISED><5:2ISED<5:3ISED> is missing a >). If a : is missing, that is easy to detect.
If the value before the : is missing, that is easy to detect.
If a character after the colon is missing, the number of characters in the payload will not match the number expected, so discard the whole packet.