Modbus Serial module don't put Log I/O Communication message

[huanghe-1]

in mango3.6.6 with modbus module 3.6.6, at application start time,don't put log i/o Communication message，neet restart the datasource,then log i/o is ok.
in mang3.7.7,any time, don't put log i/o Communication message,just put the datasource start message.
such as
2020/08/28-11:30:59,549 1598585459549 data source heartbeet test started
2020/08/28-11:43:08,536 1598586188536 data source heartbeet test started
2020/08/28-11:45:28,331 1598586328331 data source heartbeet test started
2020/08/28-11:50:34,340 1598586634340 data source heartbeet test started
2020/08/28-11:57:38,180 1598587058180 data source heartbeet test started
2020/08/28-14:30:05,532 1598596205532 data source heartbeet test started

but no Communication message