Tacotron2: bad test synthesis results

I have tried a Tacotron2 training with a custom configuration using the my own voice database
Unfortunately, the test synthesis results are not good and only 2 out of 4 test synthesis records are intelligible.
I guess that there is a very basic error causing this behavior but I couldn’t figure it out.
I hare the config file content below.

I also note that I could get very good synthesis results with Tacotron1 method and default config

Any help is appreciated.
Best Regards.

“run_name”: “ljspeech”,
“run_description”: “Tacotron2 ljspeech release training”,

    // Audio processing parameters
    "num_mels": 80,         // size of the mel spec frame. 
    "num_freq": 1025,       // number of stft frequency levels. Size of the linear spectogram frame.
    "sample_rate": 16000,   // DATASET-RELATED: wav sample-rate. If different than the original data, it is resampled.
    "frame_length_ms": 50,  // stft window length in ms.
    "frame_shift_ms": 12.5, // stft window hop-lengh in ms.
    "preemphasis": 0.98,    // pre-emphasis to reduce spec noise and make it more structured. If 0.0, no -pre-emphasis.
    "min_level_db": -100,   // normalization range
    "ref_level_db": 20,     // reference level db, theoretically 20db is the sound of air.
    "power": 1.5,           // value to sharpen wav signals after GL algorithm.
    "griffin_lim_iters": 60,// #griffin-lim iterations. 30-60 is a good range. Larger the value, slower the generation.
    // Normalization parameters
    "signal_norm": true,    // normalize the spec values in range [0, 1]
    "symmetric_norm": true, // move normalization to range [-1, 1]
    "max_norm": 4,          // scale normalization to range [-max_norm, max_norm] or [0, max_norm]
    "clip_norm": true,      // clip normalized values into the range.
    "mel_fmin": 60.0,         // minimum freq level for mel-spec. ~50 for male and ~95 for female voices. Tune for dataset!!
    "mel_fmax": 8000.0,        // maximum freq level for mel-spec. Tune for dataset!!
    "do_trim_silence": false  // enable trimming of slience of audio as you load it. LJspeech (false), TWEB (false), Nancy (true)

    "backend": "nccl",
    "url": "tcp:\/\/localhost:54321"

"reinit_layers": [],

"model": "Tacotron2",          // one of the model in models/    
"grad_clip": 1,                // upper limit for gradients for clipping.
"epochs": 1000,                // total number of epochs to train.
"lr": 0.0001,                  // Initial learning rate. If Noam decay is active, maximum learning rate.
"lr_decay": false,             // if true, Noam learning rate decaying is applied through training.
"warmup_steps": 4000,          // Noam decay steps to increase the learning rate from 0 to "lr"
"memory_size": 5,              // ONLY TACOTRON - size of the memory queue used fro storing last decoder predictions for auto-regression. If < 0, memory queue is disabled and decoder only uses the last prediction frame. 
"attention_norm": "softmax",   // softmax or sigmoid. Suggested to use softmax for Tacotron2 and sigmoid for Tacotron.
"prenet_type": "original",     // "original" or "bn".
"prenet_dropout": true,        // enable/disable dropout at prenet. 
"windowing": false,            // Enables attention windowing. Used only in eval mode.
"use_forward_attn": true,      // if it uses forward attention. In general, it aligns faster.
"forward_attn_mask": false, 
"transition_agent": false,     // enable/disable transition agent of forward attention.
"location_attn": false,        // enable_disable location sensitive attention. It is enabled for TACOTRON by default.
"loss_masking": true,         // enable / disable loss masking against the sequence padding.
"enable_eos_bos_chars": false, // enable/disable beginning of sentence and end of sentence chars.
"stopnet": true,               // Train stopnet predicting the end of synthesis. 
"separate_stopnet": true,     // Train stopnet seperately if 'stopnet==true'. It prevents stopnet loss to influence the rest of the model. It causes a better model, but it trains SLOWER.
"tb_model_param_stats": false,     // true, plots param stats per layer on tensorboard. Might be memory consuming, but good for debugging. 

"batch_size": 32,       // Batch size for training. Lower values than 32 might cause hard to learn attention. It is overwritten by 'gradual_training'.
"r": 1,                 // Number of decoder frames to predict per iteration. Set the initial values if gradual training is enabled.  
"gradual_training": null, //[[0, 7, 32], [1, 5, 32], [50000, 3, 32], [230000, 2, 16], [390000, 1, 8]], // ONLY TACOTRON - set gradual training steps [first_step, r, batch_size]. If it is null, gradual training is disabled.  
"wd": 0.000001,         // Weight decay weight.
"checkpoint": true,     // If true, it saves checkpoints per "save_step"
"save_step": 10000,      // Number of training steps expected to save traninpg stats and checkpoints.
"print_step": 25,       // Number of steps to log traning on console.
"batch_group_size": 0,  //Number of batches to shuffle after bucketing.

"run_eval": true,
"test_delay_epochs": 5,  //Until attention is aligned, testing only wastes computation time.
"test_sentences_file": null,  // set a file to load sentences to be used for testing. If it is null then we use default english sentences.
"min_seq_len": 5,       // DATASET-RELATED: minimum text length to use in training
"max_seq_len": 150,     // DATASET-RELATED: maximum text length
"output_path": "keep/",      // DATASET-RELATED: output path for all training outputs.
"num_loader_workers": 8,        // number of training data loader processes. Don't set it too big. 4-8 are good values.
"num_val_loader_workers": 4,    // number of evaluation data loader processes.
"phoneme_cache_path": "mozilla_us_phonemes",  // phoneme computation is slow, therefore, it caches results in the given folder.
"use_phonemes": true,           // use phonemes instead of raw characters. It is suggested for better pronounciation.
"phoneme_language": "en-us",     // depending on your target language, pick one from  https://github.com/bootphon/phonemizer#languages
"text_cleaner": "phoneme_cleaners",
"use_speaker_embedding": false,     // use speaker embedding to enable multi-speaker learning.
"style_wav_for_test": null,          // path to style wav file to be used in TacotronGST inference.
"use_gst": false,       // TACOTRON ONLY: use global style tokens

"datasets":   // List of datasets. They all merged and they get different speaker_ids.
            "name": "ljspeech",
            "path": "/mnt/lvm/MozillaTTS/english_tts/melissa_all_trimmed",
            "meta_file_train": "metadata_train.csv",
            "meta_file_val": "metadata_val.csv"