here is what happens, maybe related to glibc-2.29?
------------------
Application: KTorrent (ktorrent), signal: Segmentation fault
Using host libthread_db library "/lib64/libthread_db.so.1".
[Current thread is 1 (Thread 0x7f132cc7b100 (LWP 14689))]

Thread 6 (Thread 0x7f131cfcf700 (LWP 15022)):
#0 0x00007f13349b8647 in pthread_cond_timedwait@@GLIBC_2.3.2 () at /lib64/libpthread.so.0
#1 0x00007f1333b20d85 in QWaitCondition::wait(QMutex*, unsigned long) () at /usr/lib64/libQtCore.so.4
#2 0x00007f1333b15222 in () at /usr/lib64/libQtCore.so.4
#3 0x00007f1333b208c3 in () at /usr/lib64/libQtCore.so.4
#4 0x00007f13349b219c in start_thread () at /lib64/libpthread.so.0
#5 0x00007f13336af4cf in clone () at /lib64/libc.so.6

Thread 5 (Thread 0x7f131d7d0700 (LWP 15021)):
#0 0x00007f13349b8647 in pthread_cond_timedwait@@GLIBC_2.3.2 () at /lib64/libpthread.so.0
#1 0x00007f1333b20d85 in QWaitCondition::wait(QMutex*, unsigned long) () at /usr/lib64/libQtCore.so.4
#2 0x00007f1333b15222 in () at /usr/lib64/libQtCore.so.4
#3 0x00007f1333b208c3 in () at /usr/lib64/libQtCore.so.4
#4 0x00007f13349b219c in start_thread () at /lib64/libpthread.so.0
#5 0x00007f13336af4cf in clone () at /lib64/libc.so.6

Thread 4 (Thread 0x7f131dfd1700 (LWP 15020)):
#0 0x00007f13349b8647 in pthread_cond_timedwait@@GLIBC_2.3.2 () at /lib64/libpthread.so.0
#1 0x00007f1333b20d85 in QWaitCondition::wait(QMutex*, unsigned long) () at /usr/lib64/libQtCore.so.4
#2 0x00007f1333b15222 in () at /usr/lib64/libQtCore.so.4
#3 0x00007f1333b208c3 in () at /usr/lib64/libQtCore.so.4
#4 0x00007f13349b219c in start_thread () at /lib64/libpthread.so.0
#5 0x00007f13336af4cf in clone () at /lib64/libc.so.6

Thread 3 (Thread 0x7f131e7d2700 (LWP 15019)):
#0 0x00007f13349b8647 in pthread_cond_timedwait@@GLIBC_2.3.2 () at /lib64/libpthread.so.0
#1 0x00007f1333b20d85 in QWaitCondition::wait(QMutex*, unsigned long) () at /usr/lib64/libQtCore.so.4
#2 0x00007f1333b15222 in () at /usr/lib64/libQtCore.so.4
#3 0x00007f1333b208c3 in () at /usr/lib64/libQtCore.so.4
#4 0x00007f13349b219c in start_thread () at /lib64/libpthread.so.0
#5 0x00007f13336af4cf in clone () at /lib64/libc.so.6

Thread 2 (Thread 0x7f1326ce8700 (LWP 15018)):
#0 0x00007f13349b8647 in pthread_cond_timedwait@@GLIBC_2.3.2 () at /lib64/libpthread.so.0
#1 0x00007f1333b20d85 in QWaitCondition::wait(QMutex*, unsigned long) () at /usr/lib64/libQtCore.so.4
#2 0x00007f1333b15222 in () at /usr/lib64/libQtCore.so.4
#3 0x00007f1333b208c3 in () at /usr/lib64/libQtCore.so.4
#4 0x00007f13349b219c in start_thread () at /lib64/libpthread.so.0
#5 0x00007f13336af4cf in clone () at /lib64/libc.so.6

Thread 1 (Thread 0x7f132cc7b100 (LWP 14689)):
[KCrash Handler]
----------------
rebuilding libktorrent and ktorrent with glibc-2.29 doesn't help.

I would rather say it is an incompatibility between two libs like Qt and pthread, but there is no enough info to say more.

I uninstalled every multilib package (compat32): there was qt-4*compat32 package from multilib
--------------------------------
Application: KTorrent (ktorrent), signal: Segmentation fault
Using host libthread_db library "/lib64/libthread_db.so.1".
[Current thread is 1 (Thread 0x7fdbcf558100 (LWP 11624))]

Thread 2 (Thread 0x7fdbc933b700 (LWP 14259)):
#0 0x00007fdbd7295647 in pthread_cond_timedwait@@GLIBC_2.3.2 () at /lib64/libpthread.so.0
#1 0x00007fdbd63fdd85 in QWaitCondition::wait(QMutex*, unsigned long) () at /usr/lib64/libQtCore.so.4
#2 0x00007fdbd63f2222 in () at /usr/lib64/libQtCore.so.4
#3 0x00007fdbd63fd8c3 in () at /usr/lib64/libQtCore.so.4
#4 0x00007fdbd728f19c in start_thread () at /lib64/libpthread.so.0
#5 0x00007fdbd5f8c4cf in clone () at /lib64/libc.so.6

Thread 1 (Thread 0x7fdbcf558100 (LWP 11624)):
[KCrash Handler]
#6 0x0000780000000000 in ()
#7 0x00007eb705072e40 in ()
#8 0x0000000010f1a406 in ()
#9 0x0000000000000000 in ()
[Inferior 1 (process 11624) detached]
--------------------
root@drakstart64:/var/log/packages# ls | xargs grep libthread_db-1.0.so
glibc-2.29-x86_64-2:lib64/incoming/libthread_db-1.0.so
glibc-solibs-2.29-x86_64-2:lib64/incoming/libthread_db-1.0.so
-------------------
It belongs to glibc-2.29

is OK, this is not a problem. And all the other Thread 2-6 are OK.
But thread 1 is crashed. Still no info why (what's happened).
Since rebuilding did not help there are two root causes possible: 1. the software itself is buggy 2. libs used by this executable are incompatible with each other. But we still don't know which ones.

seems to be solved for current. I had to restart ktorrent 4 times before it was stable.