Quassel IRC

This is the log from yesterday evening:

2016-07-25 01:08:47 Error: unhandled Error in QSqlQuery!  
2016-07-25 01:08:47 Error:                   last Query: INSERT INTO backlog (time, bufferid, type, flags, senderid, message)VALUES (:time, :bufferid, :type, :flags, (SELECT senderid FROM sender WHERE sender = :sender), :message)  
2016-07-25 01:08:47 Error:               executed Query: INSERT INTO backlog (time, bufferid, type, flags, senderid, message)VALUES (?, ?, ?, ?, (SELECT senderid FROM sender WHERE sender = ?), ?)  
2016-07-25 01:08:47 Error:                 bound Values: :bufferid=79, :flags=4, :message='*** Looking up your hostname...', :sender='sinisalo.freenode.net', :time=1469400210, :type=2  
2016-07-25 01:08:47 Error:                 Error Number: 5  
2016-07-25 01:08:47 Error:                Error Message: database is locked Unable to fetch row  
2016-07-25 01:08:47 Error:               Driver Message: Unable to fetch row  
2016-07-25 01:08:47 Error:                   DB Message: database is locked  
2016-07-25 01:08:47 Warning: Could not connect to hackint (The remote host closed the connection)  
2016-07-25 01:08:47 Info: Client ::FFFF:590C:F1CC%0 initialized and authenticated successfully as "martin" (UserId: 8). 
2016-07-25 01:34:05 Error: unhandled Error in QSqlQuery!  
2016-07-25 01:34:05 Error:                   last Query: INSERT INTO buffer (userid, networkid, buffername, buffercname, buffertype, joined)VALUES (:userid, :networkid, :buffername, :buffercname, :buffertype, :joined)  
2016-07-25 01:34:05 Error:               executed Query: INSERT INTO buffer (userid, networkid, buffername, buffercname, buffertype, joined)VALUES (?, ?, ?, ?, ?, ?)  
2016-07-25 01:34:05 Error:                 bound Values: :buffercname='', :buffername='', :buffertype=1, :joined=0, :networkid=4, :userid=5  
2016-07-25 01:34:05 Error:                 Error Number: 5  
2016-07-25 01:34:05 Error:                Error Message: database is locked Unable to fetch row  
2016-07-25 01:34:05 Error:               Driver Message: Unable to fetch row  
2016-07-25 01:34:05 Error:                   DB Message: database is locked  
2016-07-25 01:34:05 Error: ASSERT: "!createBuffer" in file /home/sandsmark/pkg/quassel/quassel-0.12.4/src/core/coresession.cpp, line 344 
2016-07-25 01:34:06 Error: unhandled Error in QSqlQuery!  
2016-07-25 01:34:06 Error:                   last Query: INSERT INTO buffer (userid, networkid, buffername, buffercname, buffertype, joined)VALUES (:userid, :networkid, :buffername, :buffercname, :buffertype, :joined)  
2016-07-25 01:34:06 Error:               executed Query: INSERT INTO buffer (userid, networkid, buffername, buffercname, buffertype, joined)VALUES (?, ?, ?, ?, ?, ?)  
2016-07-25 01:34:06 Error:                 bound Values: :buffercname='', :buffername='', :buffertype=1, :joined=0, :networkid=9, :userid=8  
2016-07-25 01:34:06 Error:                 Error Number: 19  
2016-07-25 01:34:06 Error:                Error Message: UNIQUE constraint failed: buffer.userid, buffer.networkid, buffer.buffercname Unable to fetch row  
2016-07-25 01:34:06 Error:               Driver Message: Unable to fetch row  
2016-07-25 01:34:06 Error:                   DB Message: UNIQUE constraint failed: buffer.userid, buffer.networkid, buffer.buffercname  
2016-07-25 01:34:06 Error: ASSERT: "!createBuffer" in file /home/sandsmark/pkg/quassel/quassel-0.12.4/src/core/coresession.cpp, line 344 

Since then no one was able to connect to the core (connection refused). No log messages came after those. A simple 'server quasselcore restart' fixed it.