We generate ZPL and send the data via TCP port 9100.  About 1-5% of the time, when we send two labels at once, the first does not print.

We have not been able to reproduce the issue; it only happens at customer sites (hospitals).

Are there there any known firmware issues that might account for this? (It feels like there could be a timing issue with Ethernet or TCP receiving).

Do we need to delay between connecting and sending data?

Other info:

• Each label is about 1330 bytes of ZPL
• Printers are almost all hard-wired Ethernet
• The process is connect, send data, close connection.
• Printers are mostly ZD410 or 411

Thanks,
Cris