Modbus occasionly return -1 and errno is 33 or 138

[HEUBITLYJ]

hello， I‘m using libmodbus-3.1.8 to communication with plc， recently i met some problems with modbus write function：

here is how i create modbus tcp：
auto modbus_ctx_ = modbus_new_tcp(param.ip.c_str(), param.port); modbus_set_slave(modbus_ctx_, 1); modbus_set_response_timeout(modbus_ctx_, 0, 200000);

when i use modbus_write_bit write data to plc,
this func can return -1occasionly, the errno is 33 or 138

can someone help me to solve this problem?
thanks very much