This error happend during earling morning (04:40) where no one was using the Firebird database file.
What is this problem and what may caused it?

Motherboard: ASRock 990FX Extreme9
Processor: AMD FX(tm)-9590 Eight-Core Processor
The server has 16gb of ram (DDR3 1600MHz).
The Firebird database file is 20gb.
Only 30 simultaneous users.
The Linux server runs only Firebird 2.5.4 SuperClassic and Samba 4.1.17.
There is one SSD hard drive for Linux + Samba and other SSD hard drive for Firebird.

Debian Linux 8.2 Jessie 64 bits
Linux xxx 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt11-1+deb8u5 (2015-10-09) x86_64 GNU/Linux
Firebird TCP/IP server version LI-V2.5.4.26856 Firebird 2.5

/var/log/firebird/firebird2.5.log:
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xxx (Client)    Tue Nov  3 01:10:33 2015
        /usr/sbin/fbguard: guardian starting /usr/sbin/fb_smp_server

xxx     Tue Nov  3 04:40:42 2015
        *** DUMP ***

xxx     Tue Nov  3 04:40:42 2015
        Tag=-1 Offset=34 Length=36 Eof=0

xxx     Tue Nov  3 04:40:42 2015
        Clump 5 at offset 0: D<13><83>J<f4><e1>Z<00><a4><1e>^<00><eb><ff>Y<00><<15><00><00><1f>&]<00><1f><fe>Y<00><15>loc

xxx     Tue Nov  3 04:40:42 2015
        Fatal exception during clumplet dump: Invalid clumplet buffer structure: buffer end before end of clumplet - clumplet too long

xxx     Tue Nov  3 04:40:42 2015
        Plain dump starting with offset 34: al

xxx (Client)    Tue Nov  3 05:00:09 2015
        /usr/sbin/fbguard: /usr/sbin/fb_smp_server terminated

xxx (Client)    Tue Nov  3 05:02:09 2015
        /usr/sbin/fbguard: guardian starting /usr/sbin/fb_smp_server

xxx     Tue Nov  3 09:03:58 2015
        INET/inet_error: read errno = 104
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