Description of problem:
I logged into Plasma 5.15.5 on Wayland in an F30 KDE Plasma spin installation. I started Back in time (root) from the menu. I added a new profile to backup / . I selected to save the file permissions and extended attributes. I added /usr/src/debug and /usr/lib/debug to the exclude list. 

I started a snapshot to backup to an external USB hard drive. The snapshot stopped around 60% of the way, and Done was shown in the bottom of the screen. I had selected to check the snapshot log which showed the snapshot had stopped midway. No completed snapshot was in the list on the left of the window. I found this error in gnome-abrt later. The second time I tried this snapshot, it completed correctly without this error.

This problem with the same error and trace was reported by others at https://github.com/bit-team/backintime/issues/1003

Version-Release number of selected component:
backintime-common-1.2.0-3.fc30

Additional info:
reporter:       libreport-2.10.1
cmdline:        python3 -Es /usr/share/backintime/common/backintime.py --profile-id 3 backup
crash_function: flush
exception_type: RuntimeError
executable:     /usr/share/backintime/common/backintime.py
interpreter:    python3-3.7.4-1.fc30.x86_64
kernel:         5.1.17-300.fc30.x86_64
runlevel:       N 5
type:           Python3
uid:            0

Truncated backtrace:
snapshotlog.py:203:flush:RuntimeError: reentrant call inside <_io.BufferedWriter name='/root/.local/share/backintime/takesnapshot_3.log'>

Traceback (most recent call last):
  File "/usr/share/backintime/common/backintime.py", line 1165, in <module>
    startApp()
  File "/usr/share/backintime/common/backintime.py", line 517, in startApp
    args.func(args)
  File "/usr/share/backintime/common/backintime.py", line 739, in backup
    ret = takeSnapshot(cfg, force)
  File "/usr/share/backintime/common/backintime.py", line 94, in takeSnapshot
    ret = snapshots.Snapshots(cfg).backup(force)
  File "/usr/share/backintime/common/snapshots.py", line 692, in backup
    ret_val, ret_error = self.takeSnapshot(sid, now, include_folders)
  File "/usr/share/backintime/common/snapshots.py", line 1036, in takeSnapshot
    proc.run()
  File "/usr/share/backintime/common/tools.py", line 1981, in run
    self.callback(line, self.user_data)
  File "/usr/share/backintime/common/snapshots.py", line 809, in rsyncCallback
    self.snapshotLog.append('[C] ' + line[12:], 2)
  File "/usr/share/backintime/common/snapshotlog.py", line 195, in append
    self.logFile.write(msg + '\n')
  File "/usr/share/backintime/common/tools.py", line 1513, in handler
    self.callback()
  File "/usr/share/backintime/common/snapshotlog.py", line 203, in flush
    self.logFile.flush()
RuntimeError: reentrant call inside <_io.BufferedWriter name='/root/.local/share/backintime/takesnapshot_3.log'>

Local variables in innermost frame:
self: <snapshotlog.SnapshotLog object at 0x7faa6a4e2e10>