I hope I found the correct information;
I re-added the group before taking these logfiles. Hope that would trigger anything;
owncloud.log
{"reqId":"OsUQ3+b79rcXmxKUZjzD","remoteAddr":"208.93.152.107","app":"core","message":"Trusted domain error. \"208.93.152.107\" tried to access using \"x.x.x.x\" as host.","level":2,"time":"2017-03-01T14:08:43+00:00","method":"HEAD","url":"\/","user":"--"}
{"reqId":"uJVFSwgb1gYyT35OjPvL","remoteAddr":"208.93.152.107","app":"core","message":"Trusted domain error. \"208.93.152.107\" tried to access using \"x.x.x.x\" as host.","level":2,"time":"2017-03-01T14:08:44+00:00","method":"HEAD","url":"\/","user":"--"}
{"reqId":"SV4AW5PGQvfiu14FXkFr","remoteAddr":"198.20.69.74","app":"core","message":"Trusted domain error. \"198.20.69.74\" tried to access using \"x.x.x.x\" as host.","level":2,"time":"2017-03-01T17:06:15+00:00","method":"GET","url":"\/","user":"--"}
{"reqId":"YnPQb4HkGp0GuQMH+pNb","remoteAddr":"65.49.52.168","app":"core","message":"Trusted domain error. \"65.49.52.168\" tried to access using \"x.x.x.x\" as host.","level":2,"time":"2017-03-02T03:59:48+00:00","method":"HEAD","url":"\/index.php","user":"--"}
{"reqId":"HHdPQ2Y+95SyyfC\/rrHH","remoteAddr":"65.49.52.168","app":"core","message":"Trusted domain error. \"65.49.52.168\" tried to access using \"x.x.x.x\" as host.","level":2,"time":"2017-03-02T03:59:49+00:00","method":"GET","url":"\/admin\/images\/tango.png","user":"--"}
{"reqId":"cPV7tZ9\/YziJZkfIPaZO","remoteAddr":"192.168.10.52","app":"user_ldap","message":"Exception: {\"Exception\":\"Exception\",\"Message\":\"No user available for the given login name on 10.120.1.1:389\",\"Code\":0,\"Trace\":\"#0 \\\/var\\\/www\\\/owncloud\\\/apps\\\/user_ldap\\\/lib\\\/User_LDAP.php(120): OCA\\\\User_LDAP\\\\User_LDAP->getLDAPUserByLoginName('jill.kropivsek@...')\\n#1 \\\/var\\\/www\\\/owncloud\\\/lib\\\/private\\\/User\\\/Manager.php(200): OCA\\\\User_LDAP\\\\User_LDAP->checkPassword(*** sensitive parameters replaced ***)\\n#2 \\\/var\\\/www\\\/owncloud\\\/core\\\/Controller\\\/LoginController.php(177): OC\\\\User\\\\Manager->checkPassword(*** sensitive parameters replaced ***)\\n#3 [internal function]: OC\\\\Core\\\\Controller\\\\LoginController->tryLogin(*** sensitive parameters replaced ***)\\n#4 \\\/var\\\/www\\\/owncloud\\\/lib\\\/private\\\/AppFramework\\\/Http\\\/Dispatcher.php(159): call_user_func_array(Array, Array)\\n#5 \\\/var\\\/www\\\/owncloud\\\/lib\\\/private\\\/AppFramework\\\/Http\\\/Dispatcher.php(89): OC\\\\AppFramework\\\\Http\\\\Dispatcher->executeController(Object(OC\\\\Core\\\\Controller\\\\LoginController), 'tryLogin')\\n#6 \\\/var\\\/www\\\/owncloud\\\/lib\\\/private\\\/AppFramework\\\/App.php(99): OC\\\\AppFramework\\\\Http\\\\Dispatcher->dispatch(Object(OC\\\\Core\\\\Controller\\\\LoginController), 'tryLogin')\\n#7 \\\/var\\\/www\\\/owncloud\\\/lib\\\/private\\\/AppFramework\\\/Routing\\\/RouteActionHandler.php(46): OC\\\\AppFramework\\\\App::main('LoginController', 'tryLogin', Object(OC\\\\AppFramework\\\\DependencyInjection\\\\DIContainer), Array)\\n#8 [internal function]: OC\\\\AppFramework\\\\Routing\\\\RouteActionHandler->__invoke(Array)\\n#9 \\\/var\\\/www\\\/owncloud\\\/lib\\\/private\\\/Route\\\/Router.php(280): call_user_func(Object(OC\\\\AppFramework\\\\Routing\\\\RouteActionHandler), Array)\\n#10 \\\/var\\\/www\\\/owncloud\\\/lib\\\/base.php(891): OC\\\\Route\\\\Router->match('\\\/login')\\n#11 \\\/var\\\/www\\\/owncloud\\\/index.php(54): OC::handleRequest()\\n#12 {main}\",\"File\":\"\\\/var\\\/www\\\/owncloud\\\/apps\\\/user_ldap\\\/lib\\\/User_LDAP.php\",\"Line\":104}","level":3,"time":"2017-03-02T08:54:08+00:00","method":"POST","url":"\/index.php\/login","user":"--"}
{"reqId":"cPV7tZ9\/YziJZkfIPaZO","remoteAddr":"192.168.10.52","app":"core","message":"Login failed: 'jill.kropivsek@nl.ey.com' (Remote IP: '192.168.10.52')","level":2,"time":"2017-03-02T08:54:08+00:00","method":"POST","url":"\/index.php\/login","user":"--"}
{"reqId":"s0DmuCr0N\/oh7B6\/ZCxW","remoteAddr":"184.105.247.194","app":"core","message":"Trusted domain error. \"184.105.247.194\" tried to access using \"x.x.x.x\" as host.","level":2,"time":"2017-03-03T09:17:40+00:00","method":"GET","url":"\/","user":"--"}
{"reqId":"OnyJj31RbVYs3WdXLyO4","remoteAddr":"213.124.10.162","app":"PHP","message":"ldap_search(): Partial search results returned: Sizelimit exceeded at \/var\/www\/owncloud\/apps\/user_ldap\/lib\/LDAP.php#255","level":3,"time":"2017-03-03T09:49:10+00:00","method":"POST","url":"\/index.php\/apps\/user_ldap\/ajax\/wizard.php","user":"root"}
error.log
[Fri Mar 03 06:25:07.271815 2017] [ssl:warn] [pid 15268] AH01909: 127.0.1.1:443:0 server certificate does NOT include an ID which matches the server name
[Fri Mar 03 06:25:07.272021 2017] [mpm_prefork:notice] [pid 15268] AH00163: Apache/2.4.10 (Debian) OpenSSL/1.0.1t configured -- resuming normal operations
[Fri Mar 03 06:25:07.272028 2017] [core:notice] [pid 15268] AH00094: Command line: '/usr/sbin/apache2'
[Fri Mar 03 10:31:26.860640 2017] [authz_core:error] [pid 14917] [client 213.124.10.162:18335] AH01630: client denied by server configuration: /var/www/owncloud/data/htaccesstest.txt
[Fri Mar 03 10:48:40.362684 2017] [authz_core:error] [pid 16331] [client 213.124.10.162:18345] AH01630: client denied by server configuration: /var/www/owncloud/data/htaccesstest.txt
[Fri Mar 03 11:16:47.471785 2017] [mpm_prefork:notice] [pid 15268] AH00169: caught SIGTERM, shutting down
[Fri Mar 03 11:16:48.568497 2017] [ssl:warn] [pid 16643] AH01909: 127.0.1.1:443:0 server certificate does NOT include an ID which matches the server name
[Fri Mar 03 11:16:48.624415 2017] [ssl:warn] [pid 16644] AH01909: 127.0.1.1:443:0 server certificate does NOT include an ID which matches the server name
[Fri Mar 03 11:16:48.628813 2017] [mpm_prefork:notice] [pid 16644] AH00163: Apache/2.4.10 (Debian) OpenSSL/1.0.1t configured -- resuming normal operations
[Fri Mar 03 11:16:48.628854 2017] [core:notice] [pid 16644] AH00094: Command line: '/usr/sbin/apache2'
[Fri Mar 03 11:17:02.475143 2017] [authz_core:error] [pid 16676] [client 213.124.10.162:18379] AH01630: client denied by server configuration: /var/www/owncloud/data/htaccesstest.txt
[Fri Mar 03 11:17:51.511083 2017] [authz_core:error] [pid 16647] [client 213.124.10.162:18436] AH01630: client denied by server configuration: /var/www/owncloud/data/htaccesstest.txt
[Fri Mar 03 11:20:39.671620 2017] [authz_core:error] [pid 16649] [client 213.124.10.162:18426] AH01630: client denied by server configuration: /var/www/owncloud/data/htaccesstest.txt
[Fri Mar 03 11:32:06.617152 2017] [authz_core:error] [pid 16736] [client 213.124.10.162:18402] AH01630: client denied by server configuration: /var/www/owncloud/data/htaccesstest.txt
Access.log was empty all the time.