How is the PLC populating its string? Hopefully atomically with a CPS instruction? (Prepare string in a temporary location, then copy to Ignition-visible string using CPS.) Ignition can and will read a string’s LEN and DATA at the same time the PLC is writing, and can get the wrong length, or a partially updated character array. Ignition is generally going to read the string with a single message containing a ranged read of the containing tag. The Synchronous Copy instruction prevents a single message from seeing inconsistent data.