No answers. Just some questions...
Launch Terminal.app and enter the following diagnostic command and see what it reports about your network:
sudo changeip -checkhostname
That'll tell you some details of your local config, then whether no changes are required, or if something's amiss.
It's also possible that the server admin daemon servermgrd has wedged or crashed, and there can be various reasons for that. Check with Console.app for the logs, and see if there are any relevant or recurring errors that might point to a trigger. TCP port 311. To see if servermgrd is alive, use the following command:
sudo lsof -i -P | grep ':311'
I've seen a few cases where a reboot clears out the cruft, but that wouldn't be my first or even second resort here.
relais:~ locadmin$ sudo changeip -checkhostname
Primary address = 192.168.39.200
Current HostName = relais.local
The DNS hostname is not available, please repair DNS and re-run this tool.
dirserv:success = "success"
relais:~ locadmin$ sudo lsof -i -P | grep ':311'
The log is telling about a crash in servermgrd, which is restarted and crashing every ten seconds, a bit from the crash report
Exception Type: EXC_BREAKPOINT (SIGTRAP)
Exception Codes: 0x0000000000000002, 0x0000000000000000
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Thread 0 Crashed: Dispatch queue: com.apple.main-thread
0 com.apple.CoreFoundation 0x00007fff89aa244f __CFTypeCollectionRetain + 191
1 com.apple.CoreFoundation 0x00007fff89aabca5 __CFBasicHashAddValue + 53
2 com.apple.CoreFoundation 0x00007fff89ab3688 CFBasicHashSetValue + 184
3 com.apple.CoreFoundation 0x00007fff89ab34a7 CFDictionarySetValue + 199
4 com.apple.servermgr_dns 0x00000001031bbd66 addDataToDictionary + 2549
5 com.apple.servermgr_dns 0x00000001031bc6ec yyparse + 2324
6 com.apple.servermgr_dns 0x00000001031bd7a6 parseFile + 384
7 com.apple.servermgr_dns 0x00000001031dac19 optionsParser_lex_destroy + 104800
8 com.apple.servermgr_dns 0x00000001031d6406 optionsParser_lex_destroy + 86349
9 com.apple.servermgr_dns 0x00000001031d6468 optionsParser_lex_destroy + 86447
10 com.apple.servermgr_dns 0x00000001031ce904 optionsParser_lex_destroy + 54859
11 com.apple.servermgr_dns 0x00000001031cea41 optionsParser_lex_destroy + 55176
12 com.apple.servermgr_dns 0x00000001031d19c8 optionsParser_lex_destroy + 67343
13 com.apple.servermgr_dns 0x00000001031c1f78 optionsParser_lex_destroy + 3263
14 com.apple.servermgr_dns 0x00000001031c67db optionsParser_lex_destroy + 21794
15 com.apple.servermgr_dns 0x00000001031c254b optionsParser_lex_destroy + 4754
16 libservermgrcommon.dylib 0x000000010003ec18 -[BundleManager init] + 402
17 libservermgrcommon.dylib 0x000000010003dd9d +[BundleManager defaultManager] + 51
18 com.apple.ServerManagerDaemon 0x0000000100003bcb 0x100000000 + 15307
19 com.apple.ServerManagerDaemon 0x00000001000014c0 0x100000000 + 5312
So it looks like there is some t=file that is now not exactly like the parser wants it.
Ok, this crash report gave the clues. There was a malformed entry in one of the zone files, so it was a matter of disabling records until Server Admin started working again.
THanks for the pointers
P.S. For some peculiar reason I got two userbnames here with the same Apple ID. Could be me logging in from different computers and a strict cooky policy, but I am no caring about that.