MariaDB didn't respond on any new connect and the connected clients hung.
The attachement contains the complete errorlog.
The incident occured at about "180410 7:30:00" and lasted until "180410 8:50:51".
Here is an excerpt of the errorlog:

180221 12:12:55 InnoDB: Waiting for the background threads to start
180221 12:12:56 Percona XtraDB (http://www.percona.com) 5.5.52-MariaDB-38.3 started; log sequence number 41289080384741
180221 12:12:56 [Note] Plugin 'FEEDBACK' is disabled.
180221 12:12:56 [Note] Server socket created on IP: '::'.
180221 12:12:56 [Note] Event Scheduler: Loaded 0 events
180221 12:12:56 [Note] d:\leutek\mariadb\bin\mysqld.exe: bereit für Verbindungen.
Version: '5.5.54-MariaDB' Socket: '' Port: 3306 mariadb.org binary distribution
180221 12:18:24 [ERROR] mysqld.exe: Tabelle '.\zislog\log_20180221' ist als defekt markiert und sollte repariert werden
180221 12:18:24 [Warning] Checking table: '.\zislog\log_20180221'
180307 1:00:00 [ERROR] Table status/currenteustatus20180307 contains 3 indexes inside InnoDB, which is different from the number of indexes 2 defined in the MySQL
180405 10:06:55 [Warning] option 'innodb-additional-mem-pool-size': signed value 3221225472 adjusted to 2147482624
180405 10:06:55 InnoDB: The InnoDB memory heap is disabled
180405 10:06:55 InnoDB: Mutexes and rw_locks use Windows interlocked functions
180405 10:06:55 InnoDB: Compressed tables use zlib 1.2.3
180405 10:06:55 InnoDB: Initializing buffer pool, size = 384.0G
180405 10:07:23 InnoDB: Completed initialization of buffer pool
180405 10:08:57 InnoDB: highest supported file format is Barracuda.
InnoDB: The log sequence number in ibdata files does not match
InnoDB: the log sequence number in the ib_logfiles!
180405 10:08:59 InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer...
180405 10:09:20 InnoDB: Waiting for the background threads to start
180405 10:09:21 Percona XtraDB (http://www.percona.com) 5.5.52-MariaDB-38.3 started; log sequence number 42609915647300
180405 10:09:21 [Note] Plugin 'FEEDBACK' is disabled.
180405 10:09:21 [Note] Server socket created on IP: '::'.
180405 10:09:21 [Note] Event Scheduler: Loaded 0 events
180405 10:09:21 [Note] d:\leutek\mariadb\bin\mysqld.exe: bereit für Verbindungen.
Version: '5.5.54-MariaDB' Socket: '' Port: 3306 mariadb.org binary distribution
180405 10:14:49 [ERROR] mysqld.exe: Tabelle '.\zislog\log_20180405' ist als defekt markiert und sollte repariert werden
180405 10:14:49 [Warning] Checking table: '.\zislog\log_20180405'
InnoDB: Warning: a long semaphore wait:
--Thread 8668 has waited at log0log.ic line 320 for 258.00 seconds the semaphore:
Mutex at 0000000012B1FD58 '&log_sys->mutex', lock var 0
waiters flag 0
InnoDB: Warning: a long semaphore wait:
--Thread 8208 has waited at row0upd.c line 2177 for 257.00 seconds the semaphore:
X-lock (wait_ex) on RW-latch at 00000003AABE7ED0 '&block->lock'
a writer (thread id 8208) has reserved it in mode exclusive
number of readers 0, waiters flag 1, lock_word: 0
Last time read locked in file row0sel.c line 4046
Last time write locked in file D:\winx64-packages\build\src\storage\xtradb\row\row0upd.c line 2177
InnoDB: Warning: a long semaphore wait:
--Thread 8528 has waited at row0sel.c line 4046 for 250.00 seconds the semaphore:
S-lock on RW-latch at 00000003AABE7ED0 '&block->lock'
a writer (thread id 8208) has reserved it in mode exclusive
number of readers 0, waiters flag 1, lock_word: 0
Last time read locked in file row0sel.c line 4046
Last time write locked in file D:\winx64-packages\build\src\storage\xtradb\row\row0upd.c line 2177
InnoDB: Warning: a long semaphore wait:
--Thread 17280 has waited at log0log.ic line 320 for 242.00 seconds the semaphore:
Mutex at 0000000012B1FD58 '&log_sys->mutex', lock var 0
waiters flag 0
InnoDB: Warning: a long semaphore wait:
--Thread 9788 has waited at trx0sys.ic line 154 for 242.00 seconds the semaphore:
X-lock (wait_ex) on RW-latch at 00000003C900EB00 '&block->lock'
a writer (thread id 9788) has reserved it in mode exclusive
number of readers 0, waiters flag 0, lock_word: 0
Last time read locked in file buf0flu.c line 1340
Last time write locked in file D:\winx64-packages\build\src\storage\xtradb\include\trx0sys.ic line 154
InnoDB: Warning: a long semaphore wait:
--Thread 9356 has waited at srv0srv.c line 2835 for 242.00 seconds the semaphore:
Mutex at 0000000000326E78 '&kernel_mutex', lock var 1
waiters flag 1
InnoDB: Warning: a long semaphore wait:
--Thread 19932 has waited at trx0trx.c line 924 for 242.00 seconds the semaphore:
Mutex at 0000000000326E78 '&kernel_mutex', lock var 1
waiters flag 1
InnoDB: Warning: a long semaphore wait:
--Thread 15288 has waited at trx0trx.c line 924 for 241.00 seconds the semaphore:
Mutex at 0000000000326E78 '&kernel_mutex', lock var 1
waiters flag 1
InnoDB: Warning: a long semaphore wait:
--Thread 9416 has waited at trx0trx.c line 924 for 241.00 seconds the semaphore:
Mutex at 0000000000326E78 '&kernel_mutex', lock var 1
waiters flag 1
InnoDB: Warning: semaphore wait:
--Thread 8668 has waited at log0log.ic line 320 for 258.00 seconds the semaphore:
Mutex at 0000000012B1FD58 '&log_sys->mutex', lock var 0
waiters flag 0
180410 8:50:51 [Note] d:\leutek\mariadb\bin\mysqld.exe: Normal heruntergefahren
180410 8:50:51 [Note] Event Scheduler: Purging the queue. 0 events
180410 9:02:38 [Warning] option 'innodb-additional-mem-pool-size': signed value 3221225472 adjusted to 2147482624
180410 9:02:38 InnoDB: The InnoDB memory heap is disabled
180410 9:02:38 InnoDB: Mutexes and rw_locks use Windows interlocked functions