I am trying to use dolphin 16.12.3 but it does not appear on the screen, so you get only a process running in background. I don't know at the moment if the bug is reproducible, since it is the first time I experience it, and I am using such Dolphin version since many days.
Plasma 5.9.4


$ gdb dolphin 8514
GNU gdb (GDB) Fedora 7.12.1-47.fc25
Type "apropos word" to search for commands related to "word"...
Reading symbols from dolphin...Reading symbols from /usr/lib/debug/usr/bin/dolphin.debug...done.
done.
Attaching to program: /usr/bin/dolphin, process 8514
[New LWP 8515]
[New LWP 8516]
[New LWP 8517]
[New LWP 8518]
[New LWP 8519]
[New LWP 8520]
[New LWP 8521]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
0x00007fcb64f4c81d in nanosleep () at ../sysdeps/unix/syscall-template.S:84
84      T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) continue
Continuing.
(After 5 minutes)
^C
Thread 1 "dolphin" received signal SIGINT, Interrupt.
0x00007fcb64f4c81d in nanosleep () at ../sysdeps/unix/syscall-template.S:84
84      T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) bt
#0  0x00007fcb64f4c81d in nanosleep () at ../sysdeps/unix/syscall-template.S:84
#1  0x00007fcb65c2bb8d in qt_nanosleep(timespec) (amount=...) at tools/qelapsedtimer_unix.cpp:193
#2  0x00007fcb65b93dc8 in QThread::msleep(unsigned long) (msecs=msecs@entry=50) at thread/qthread_unix.cpp:506
#3  0x00007fcb676e2cd8 in KDirWatchPrivate::useFAM(KDirWatchPrivate::Entry*) (this=this@entry=0x56251d9918d0, e=e@entry=0x56251d8a84e0)
    at /usr/src/debug/kcoreaddons-5.33.0/src/lib/io/kdirwatch.cpp:696
#4  0x00007fcb676e306a in KDirWatchPrivate::addWatch(KDirWatchPrivate::Entry*) (this=this@entry=0x56251d9918d0, e=e@entry=0x56251d8a84e0)
    at /usr/src/debug/kcoreaddons-5.33.0/src/lib/io/kdirwatch.cpp:979
#5  0x00007fcb676e3c33 in KDirWatchPrivate::addEntry(KDirWatch*, QString const&, KDirWatchPrivate::Entry*, bool, QFlags<KDirWatch::WatchMode>) (this=0x56251d9918d0, instance=instance@entry=0x56251d89f770, _path=..., sub_entry=<optimized out>, sub_entry@entry=0x0, isDir=isDir@entry=false, watchModes=..., watchModes@entry=...)
    at /usr/src/debug/kcoreaddons-5.33.0/src/lib/io/kdirwatch.cpp:936
#6  0x00007fcb676e5e13 in KDirWatch::addFile(QString const&) (this=this@entry=0x56251d89f770, _path=...)
    at /usr/src/debug/kcoreaddons-5.33.0/src/lib/io/kdirwatch.cpp:1891
#7  0x00007fcb69d91dbd in KBookmarkManager::KBookmarkManager(QString const&) (this=0x56251d89ce60, bookmarksFile=...)
    at /usr/src/debug/kbookmarks-5.33.0/src/kbookmarkmanager.cpp:293
#8  0x00007fcb69d921e8 in KBookmarkManager::managerForExternalFile(QString const&) (bookmarksFile=...)
    at /usr/src/debug/kbookmarks-5.33.0/src/kbookmarkmanager.cpp:226
#9  0x00007fcb6bc0cbc5 in KFilePlacesModel::KFilePlacesModel(QObject*) (this=0x56251d803a10, parent=<optimized out>)
    at /usr/src/debug/kio-5.33.0/src/filewidgets/kfileplacesmodel.cpp:93
#10 0x00007fcb6c5fc1c6 in DolphinViewContainer::DolphinViewContainer(QUrl const&, QWidget*) (this=0x56251d88d800, url=..., parent=<optimized out>)
    at /usr/src/debug/dolphin-16.12.3/src/dolphinviewcontainer.cpp:72
#11 0x00007fcb6c603d5c in DolphinTabPage::createViewContainer(QUrl const&) const (this=this@entry=0x56251d8870d0, url=...)
    at /usr/src/debug/dolphin-16.12.3/src/dolphintabpage.cpp:340
#12 0x00007fcb6c603f93 in DolphinTabPage::DolphinTabPage(QUrl const&, QUrl const&, QWidget*) (this=0x56251d8870d0, primaryUrl=..., secondaryUrl=..., parent=<optimize---Type <return> to continue, or q <return> to quit---
d out>) at /usr/src/debug/dolphin-16.12.3/src/dolphintabpage.cpp:42
#13 0x00007fcb6c605a95 in DolphinTabWidget::openNewTab(QUrl const&, QUrl const&) (this=this@entry=0x56251d4a4960, primaryUrl=..., secondaryUrl=...)
    at /usr/src/debug/dolphin-16.12.3/src/dolphintabwidget.cpp:143
#14 0x00007fcb6c605f26 in DolphinTabWidget::openDirectories(QList<QUrl> const&, bool) (this=0x56251d4a4960, dirs=..., splitView=false)
    at /usr/src/debug/dolphin-16.12.3/src/dolphintabwidget.cpp:169
#15 0x00007fcb6c5efb7c in DolphinMainWindow::openDirectories(QList<QUrl> const&, bool) (this=<optimized out>, dirs=..., splitView=<optimized out>)
    at /usr/src/debug/dolphin-16.12.3/src/dolphinmainwindow.cpp:177
#16 0x00007fcb6c60a41d in kdemain(int, char**) (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/dolphin-16.12.3/src/main.cpp:136
#17 0x00007fcb64ea0401 in __libc_start_main (main=
    0x56251bd09b10 <main>, argc=1, argv=0x7fff2ea2a4e8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fff2ea2a4d8)
    at ../csu/libc-start.c:289
#18 0x000056251bd09b4a in _start ()
(gdb)