/me has to retract comment #13, it is indeed the app printing the message. Camera app has 2 threads printing it

sudo strace -f -e write -p `pidof camera-app` 2>&1 | grep ust
[pid 14107] write(2, "libust[14085/14107]: Error: Erro"..., 114 <unfinished ...>
[pid 14106] write(2, "libust[14085/14106]: Error: Erro"..., 108) = 108

and looking at the threads involved:

(gdb) i thre
  Id   Target Id         Frame 
  20   Thread 0xb2f67410 (LWP 14097) "RPC Thread" 0xb64ca4e2 in poll () at ../sysdeps/unix/syscall-template.S:81
  19   Thread 0xb23e1410 (LWP 14099) "arch_worker" 0xb46ab840 in ?? ()
  18   Thread 0xb2442b40 (LWP 14100) "camera-app" __libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:47
  17   Thread 0xb19ff410 (LWP 14101) "SWD-GPU Job" __libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46
  16   Thread 0xb11ff410 (LWP 14102) "SWD-Frame" __libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46
  15   Thread 0xb07bb410 (LWP 14104) "QQmlThread" 0xb64ca4e2 in poll () at ../sysdeps/unix/syscall-template.S:81
  14   Thread 0xae6b2410 (LWP 14106) "QQmlThread" 0xb64ae4e2 in nanosleep () at ../sysdeps/unix/syscall-template.S:81
  13   Thread 0xadeb2410 (LWP 14107) "QQmlThread" 0xb64ae4e2 in nanosleep () at ../sysdeps/unix/syscall-template.S:81
  12   Thread 0xad0ff410 (LWP 14110) "gdbus" 0xb64ca4e2 in poll () at ../sysdeps/unix/syscall-template.S:81
  11   Thread 0xab97a410 (LWP 14112) "camera-app" __libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46
  10   Thread 0xa9faa410 (LWP 14117) "QQuickPixmapRea" 0xb64ca4e2 in poll () at ../sysdeps/unix/syscall-template.S:81
  9    Thread 0xa9223410 (LWP 14118) "Input dispatch" 0xb64ca4e2 in poll () at ../sysdeps/unix/syscall-template.S:81
  8    Thread 0xa83ff410 (LWP 14124) "camera-app" 0xb64d1132 in epoll_wait () at ../sysdeps/unix/syscall-template.S:81
  7    Thread 0xa7bff410 (LWP 14126) "QSGRenderThread" __libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46
  6    Thread 0xa73ff410 (LWP 14127) "Swap Worker" __libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46
  5    Thread 0xa63ff410 (LWP 14128) "camera-app" 0xb46ac9f4 in ?? ()
  4    Thread 0xa5bff410 (LWP 14140) "Binder_1" 0xb46ab840 in ?? ()
  3    Thread 0xa53ff410 (LWP 14141) "Binder_2" 0xb46ab840 in ?? ()
  2    Thread 0xa4bff410 (LWP 14172) "Binder_3" 0xb46ab840 in ?? ()
* 1    Thread 0xb6f32000 (LWP 14085) "camera-app" __libc_do_syscall () at ../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:46
(gdb) t 14
[Switching to thread 14 (Thread 0xae6b2410 (LWP 14106))]
#0  0xb64ae4e2 in nanosleep () at ../sysdeps/unix/syscall-template.S:81
81	../sysdeps/unix/syscall-template.S: No such file or directory.
(gdb) bt
#0  0xffffffff in nanosleep () at ../sysdeps/unix/syscall-template.S:81
#1  0xffffffff in __sleep (seconds=0) at ../sysdeps/unix/sysv/linux/sleep.c:138
#2  0xffffffff in  () at /usr/lib/arm-linux-gnueabihf/liblttng-ust.so.0
(gdb) t 13
[Switching to thread 13 (Thread 0xadeb2410 (LWP 14107))]
#0  0xb64ae4e2 in nanosleep () at ../sysdeps/unix/syscall-template.S:81
81	in ../sysdeps/unix/syscall-template.S
(gdb) bt
#0  0xffffffff in nanosleep () at ../sysdeps/unix/syscall-template.S:81
#1  0xffffffff in __sleep (seconds=0) at ../sysdeps/unix/sysv/linux/sleep.c:138
#2  0xffffffff in  () at /usr/lib/arm-linux-gnueabihf/liblttng-ust.so.0
(gdb) 

Still dunno what exact project is responsible