I do not see any entries in the logs that I can make out to be a 12 hour pattern.
On February 9th there are a series of logins and logouts - sometimes just a few minutes apart. Was that you doing some testing?
Also:
2020-10-20 20:33:08 [Alert][Alarm-Log] AlarmID:104105,AlarmLevel:Alert,Voice Register Fail Alarm, Other Error: Start
2020-10-20 20:38:14 [Alert][Alarm-Log] AlarmID:104105,AlarmLevel:Alert,Voice Register Fail Alarm, Other Error: Resume
1981-01-01 00:00:15 [Error][Alarm-Log] AlarmID:104001,AlarmLevel:Error,Device reset. Cause: ONU reset after being powered on, Terminal:OTHER
1981-01-01 00:00:14 [Error][Alarm-Log] AlarmID:104001,AlarmLevel:Error,Device reset. Cause: ONU reset after being powered on, Terminal:OTHER
1981-01-01 00:00:14 [Error][Alarm-Log] AlarmID:104001,AlarmLevel:Error,Device reset. Cause: ONU reset after being powered on, Terminal:OTHER
1981-01-01 00:00:14 [Error][Alarm-Log] AlarmID:104001,AlarmLevel:Error,Device reset. Cause: ONU reset after being powered on, Terminal:OTHER
Are those resets that you initiated via power off/power on?
And:
Terminal:WEB(192.168.100.103),Result:Success,Type:Set,WANConnectionDevice.WANPPPConnection.PortMapping:1.2.1.1,PortMappingEnabled:1,PortMappingDescription:Minecraft,InternalClient:192.168.100.103,...
2020-03-13 21:40:56 [Critical][Config-Log] Terminal:WEB(192.168.100.103),Result:Success,Type:Set,WANConnectionDevice.WANPPPConnection.PortMapping:1.2.1.2,PortMappingEnabled:1,PortMappingDescription:Minecraft 2,...
There were similar entries via 192.168.100.93 also in the log.
Are you hosting or attempting to host a Minecraft server?
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Does the following link present the User Manual matching your Huawei HG8245H
https://setuprouter.com/router/huawei/hg8245h/manual-1982.pdf
[Do verify that I found the correct manual.]
And your home physical setup/configuration is similar to Figure 2-14 on physically numbered Page 2-14.
What other devices, if any, are connected? Telephones, printer, NAS?
The router appears to be at its default setting of 192.168.100.1
I noted two devices connecting that were being provided DHCP IP addresses of 192.168.100.103 and 192.168.100.105.
".103" (Minecraft Servers) being far more frequent. Seeing no other DHCP addresses being assigned makes me believe there are no other devices.
Exception being the 192.168.100.93 assignment.... which could have been the same device - being DHCP.
Overall, if you are hosting a Minecraft server you need to assign it a Static IP that is outside of the DHCP IP address range reserved for the router's DHCP assignments.
And that Static IP address should be reserved on the router via the host MAC.
Certainly does not explain the 12 hour resets per se but I am wondering about an overall misconfiguration issue.