This implies that you are having trouble with a serial connection. It would be helpful if you did directly answer the questions I asked, but if my assumption here is correct, the problem is likely related to the serial connection/parameters, and not specifically an OpenWrt issue. For example, it could be a physical issue (such as a poor connection or missing ground or the wrong voltage), an issue with the USB-serial adapter you are using (an unreliable chip or bad drivers), or the connection parameters (likely just baud rate, but could be other things).
For the benefit of future readers who may experience similar things, it would be good if you could elaborate about what you did to solve/bypass the issue.
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