Sounds like the hardware is probably fine, but the NS1 serial server settings or UART timing is causing the issue. If your PC only receives MCU data after sending multiple times, usually it’s one of these problems:

• Baud rate mismatch
• Wrong flow control setting
• Serial buffer delay in NS1
• TCP packet merge / timeout issue
• UART framing mismatch (data bits, parity, stop bits)

First, double-check that the PC, NS1, and MCU all use the exact same UART settings:

• Same baud rate
• 8N1 usually
• Flow control OFF unless you wired RTS/CTS

Then check the NS1 serial server config:

• Disable packet packing or “data frame timeout”
• Reduce serial buffering delay
• Enable low-latency mode if available
• Try TCP Server mode first instead of UDP

Another super common issue is the MCU sending too fast right after boot. The NS1 may not finish socket initialization yet, so the first packets get dropped. Add a small startup delay on the MCU side like 500ms–2s before UART transmit.

Also test with a serial tool like Hercules or TCP Test Tool and send continuous data instead of single packets. If continuous streaming works but single messages fail, it’s almost definitely a packet timeout/buffering config issue inside the NS1.

One more thing — if the MCU UART uses interrupt RX/TX, check whether the transmit buffer is actually flushing completely. A lot of MCU UART drivers silently lose the first byte sometimes.