Thanks! I did finally find the file in the LaunchDeamons or LaunchAgents folder. But, unfortunately, that wasn't the issue... ;-)
It still wakes up a couple of times in the night, as one can see in the log file. And I don't see a common thread in those wakeups besides the "ASL Sender Statistics", which I have not find anything about...
Jan 3 04:56:51 Stefans-MBP15 syslogd[51]: ASL Sender Statistics
Jan 3 04:56:51 Stefans-MacBook-Pro15 com.apple.xpc.launchd[1] (com.apple.bsd.dirhelper[790]): Endpoint has been activated through legacy launch(3) APIs. Please switch to XPC or bootstrap_check_in(): com.apple.bsd.dirhelper
Jan 3 04:56:51 Stefans-MacBook-Pro15 Dropbox[462]: [0103/045651.383186:WARNING:dns_config_service_posix.cc(326)] Failed to read DnsConfig.
Jan 3 04:56:53 Stefans-MBP15 systemstats[62]: assertion failed: 17G2208: systemstats + 914800 [D1E75C38-62CE-3D77-9ED3-5F6D38EF0676]: 0x40
Jan 3 04:56:53 Stefans-MBP15 timed[90]: settimeofday({0x5c2d8805,0xb6b34}) == 0
Jan 3 04:56:53 Stefans-MBP15 com.apple.xpc.launchd[1] (com.apple.imfoundation.IMRemoteURLConnectionAgent): Unknown key for integer: _DirtyJetsamMemoryLimit
Jan 3 04:56:56 Stefans-MBP15 xpcproxy[829]: libcoreservices: _dirhelper_userdir: 529: bootstrap_look_up returned (ipc/send) invalid destination port
Jan 3 04:56:56 Stefans-MBP15 netbiosd[829]: DEPRECATED USE in libdispatch client: Setting timer interval to 0 requests a 1ns timer, did you mean FOREVER (a one-shot timer)?
Jan 3 06:11:36 Stefans-MBP15 syslogd[51]: ASL Sender Statistics
Jan 3 06:11:36 Stefans-MacBook-Pro15 Dropbox[462]: [0103/061136.488421:WARNING:dns_config_service_posix.cc(326)] Failed to read DnsConfig.
Jan 3 06:11:38 Stefans-MBP15 systemstats[62]: assertion failed: 17G2208: systemstats + 914800 [D1E75C38-62CE-3D77-9ED3-5F6D38EF0676]: 0x40
Jan 3 06:11:38 Stefans-MBP15 timed[90]: settimeofday({0x5c2d998a,0xcc470}) == 0
Jan 3 06:11:41 Stefans-MBP15 xpcproxy[842]: libcoreservices: _dirhelper_userdir: 529: bootstrap_look_up returned (ipc/send) invalid destination port
Jan 3 06:11:41 Stefans-MBP15 netbiosd[842]: DEPRECATED USE in libdispatch client: Setting timer interval to 0 requests a 1ns timer, did you mean FOREVER (a one-shot timer)?
Jan 3 06:12:43 Stefans-MBP15 dsmcad[86]: Set wake up time for 3. January 2019 at 07:29:43 CET.
Jan 3 06:21:36 Stefans-MBP15 com.apple.xpc.launchd[1] (com.apple.xpc.launchd.domain.user.502): Service "com.apple.xpc.launchd.unmanaged.loginwindow.101" tried to register for endpoint "com.apple.tsm.uiserver" already registered by owner: com.apple.SystemUIServer.agent
Jan 3 06:21:36 Stefans-MBP15 syslogd[51]: ASL Sender Statistics
Jan 3 06:21:36 Stefans-MBP15 com.apple.xpc.launchd[1] (com.apple.xpc.launchd.domain.user.502): Service "com.apple.xpc.launchd.unmanaged.loginwindow.101" tried to register for endpoint "com.apple.tsm.uiserver" already registered by owner: com.apple.SystemUIServer.agent
Jan 3 07:00:23 Stefans-MBP15 syslogd[51]: ASL Sender Statistics
Jan 3 07:00:23 Stefans-MacBook-Pro15 Dropbox[462]: [0103/070023.493062:WARNING:dns_config_service_posix.cc(326)] Failed to read DnsConfig.
Jan 3 07:00:25 Stefans-MBP15 systemstats[62]: assertion failed: 17G2208: systemstats + 914800 [D1E75C38-62CE-3D77-9ED3-5F6D38EF0676]: 0x40
Jan 3 07:00:25 Stefans-MBP15 com.apple.xpc.launchd[1] (com.apple.imfoundation.IMRemoteURLConnectionAgent): Unknown key for integer: _DirtyJetsamMemoryLimit
Jan 3 07:00:28 Stefans-MBP15 xpcproxy[860]: libcoreservices: _dirhelper_userdir: 529: bootstrap_look_up returned (ipc/send) invalid destination port
Jan 3 07:00:28 Stefans-MBP15 netbiosd[860]: DEPRECATED USE in libdispatch client: Setting timer interval to 0 requests a 1ns timer, did you mean FOREVER (a one-shot timer)?
Any idea?