In some apps (like virtualbox or vlc) this erro roccurs when starting app:
Qt FATAL: This application failed to start because it could not find or load the Qt platform plugin "xcb"
Available platform plugins are: minimal, offscreen, xcb.
Reinstalling the application may fix this problem.
Manually running "pkg upgrade -f qt5-gui" helps, but it is IMHO a problem/bug.
Look at: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=214339
*** Bug 214339 has been marked as a duplicate of this bug. ***
Same problem and solution with ports-mgmt/portrac.
I think there is something missing in the Makefile USE_QT5= gui does not help. Maybe any LIB_BEPENDS?
*** Bug 214474 has been marked as a duplicate of this bug. ***
This solution *kind of* worked.
"pkg upgrade" alone was not finding any upgrades since last time and the latest version I always got was "qt5-gui-5.6.2", which causes the problem.
So I had to manually download the "qt5-gui-5.6.2_1.txz" file from the servers and then "pkg add" it.
Even now, running "pkg upgrade -f qt5-gui" wants to downgrade the working 5.6.2_1 version and install version 5.6.2.
I manually bumped PORTREVISION in qt5-gui in ports r425987 to trigger a rebuild (it's still unclear to me how the xcb part of qt5-gui depends on perl). The repository problems mentioned in comment #4 look unrelated to this specific issue.