Encountered Compute CTC targets failed for *.lstmf error when using correct png and gt.txt files

[yctong]

$ make training MODEL_NAME=NotoSans-Bold START_MODEL=eng TESSDATA=../tessdata/ MAX_ITERATIONS=100 LEARNING_RATE=0.001
You are using make version: 4.4.1

lstmtraining \
  --debug_interval 0 \
  --traineddata data/NotoSans-Bold/NotoSans-Bold.traineddata \
  --old_traineddata ../tessdata//eng.traineddata \
  --continue_from data/eng/NotoSans-Bold.lstm \
  --learning_rate 0.001 \
  --model_output data/NotoSans-Bold/checkpoints/NotoSans-Bold \
  --train_listfile data/NotoSans-Bold/list.train \
  --eval_listfile data/NotoSans-Bold/list.eval \
  --max_iterations 100 \
  --target_error_rate 0.01 \
2>&1 | tee -a data/NotoSans-Bold/training.log
Loaded file data/eng/NotoSans-Bold.lstm, unpacking...
Warning: LSTMTrainer deserialized an LSTMRecognizer!
Code range changed from 111 to 111!
Num (Extended) outputs,weights in Series:
  1,36,0,1:1, 0
Num (Extended) outputs,weights in Series:
  C3,3:9, 0
  Ft16:16, 160
Total weights = 160
  [C3,3Ft16]:16, 160
  Mp3,3:16, 0
  TxyLfys64:64, 20736
  Lfx96:96, 61824
  RxLrx96:96, 74112
  Lfx512:512, 1247232
  Fc111:111, 56943
Total weights = 1461007
Previous null char=110 mapped to 110
Continuing from data/eng/NotoSans-Bold.lstm
Compute CTC targets failed for data/NotoSans-Bold-ground-truth/eng_19.lstmf!
Compute CTC targets failed for data/NotoSans-Bold-ground-truth/eng_53.lstmf!
Compute CTC targets failed for data/NotoSans-Bold-ground-truth/eng_21.lstmf!
Compute CTC targets failed for data/NotoSans-Bold-ground-truth/eng_17.lstmf!
Compute CTC targets failed for data/NotoSans-Bold-ground-truth/eng_16.lstmf!
Compute CTC targets failed for data/NotoSans-Bold-ground-truth/eng_47.lstmf!

"Compute CTC targets failed for xxx" error was encountered while running the above command. My PNG and TXT files are correct, containing a single line of text. The LSTMF and BOX files are also generated; however, the BOX file includes an extra line with no characters. I've attached the BOX file (renamed with a .txt extension for uploading).

eng_0.box.txt
eng_0.gt.txt