I don't know exactly when it happens, but I observed this after suspend/resume and attaching an additional monitor:

Program received signal SIGSEGV, Segmentation fault.
__strcmp_sse2 () at ../sysdeps/x86_64/multiarch/../strcmp.S:213
213     ../sysdeps/x86_64/multiarch/../strcmp.S: Datei oder Verzeichnis nicht gefunden.
(gdb) bt
#0  __strcmp_sse2 () at ../sysdeps/x86_64/multiarch/../strcmp.S:213
#1  0x00007f3180c9d617 in transcmp (p1=0x7fff3f799aa0, p2=0xd1e1a0) at dcigettext.c:240
#2  0x00007f3180d52c02 in __tfind (key=0x7fff3f799aa0, vrootp=<optimized out>,
    compar=0x7f3180c9d5f0 <transcmp>) at tsearch.c:321
#3  0x00007f3180c9e3ca in __dcigettext (domainname=0xd56af0 "xfce4-netload-plugin", 
    msgid1=0x2 <Address 0x2 out of bounds>, msgid2=0x0, plural=0, n=0, category=5) at dcigettext.c:485
#4  0x00000000004095b7 in format_byte_humanreadable (string=0x7fff3f79fc30 "4,00 ", stringsize=8192, 
    number=<optimized out>, digits=2) at utils.c:151
#5  0x0000000000408a15 in update_monitors (global=0xd56a20) at netload.c:241
#6  update_monitors (global=0xd56a20) at netload.c:147
#7  0x00007f318148a5ab in g_timeout_dispatch (source=0xe021b0, callback=<optimized out>, 
    user_data=<optimized out>) at gmain.c:3882
#8  0x00007f31814899e3 in g_main_dispatch (context=0xd561c0) at gmain.c:2539
#9  g_main_context_dispatch (context=0xd561c0) at gmain.c:3075
#10 0x00007f3181489d30 in g_main_context_iterate (dispatch=1, block=<optimized out>, context=0xd561c0, 
    self=<optimized out>) at gmain.c:3146
#11 g_main_context_iterate (context=0xd561c0, block=<optimized out>, dispatch=1, self=<optimized out>)
    at gmain.c:3083
#12 0x00007f318148a12a in g_main_loop_run (loop=0xe0c790) at gmain.c:3340
#13 0x00007f31826deac7 in IA__gtk_main () at gtkmain.c:1257
#14 0x0000000000405200 in main (argc=8, argv=0x7fff3f7aff68) at netload.c:1264


utils.c:151
    /* Add the unit name */
--> g_strlcat(string, _(unit_names[uidx]), stringsize);

=>

diff --git a/panel-plugin/utils.c b/panel-plugin/utils.c
index 30647af..c546803 100644
--- a/panel-plugin/utils.c
+++ b/panel-plugin/utils.c
@@ -97,7 +97,7 @@ char* format_byte_humanreadable(char* string, int stringsize, double number, int
     }
 
     /* calculate number and appropriate unit size for display */
-    while(number_displayed >= 1024.0 && uidx < sizeof(unit_names))
+    while(number_displayed >= 1024.0 && uidx < sizeof(unit_names) - 1)
     {
         number_displayed /= 1024.0;
         uidx++;
--

uidx == sizeof(unit_names) would be out of bounds, right?