Lots of "... contains unknown char/phoneme...Symbol will be skipped." warnings popping up.
I tried to train a fastpitch model on the Blizzard 2013 dataset. When I started the training, lots of such warnings kept popping up, for example, 
```
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [And then on her BRIY1FLIY0 IH0KSPREH1SIH0NG HHER1 sorrow for what HHIY1 must have suffered, HHIY1 replied,] contains unknown char/phoneme: [A].Original text: [And then on her briefly expressing her sorrow for what he must have suffered, he replied,]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [How different from what it was the last two dances.] contains unknown char/phoneme: [H].Original text: [How different from what it was the last two dances.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [which was VEH1RIY0 LIH1TAH0L relieved by the long speeches of MIH1STER0 Collins.] contains unknown char/phoneme: [C].Original text: [which was very little relieved by the long speeches of mister Collins.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [Henry is different. He LAH1VZ to be DUW1IH0NG.] contains unknown char/phoneme: [H].Original text: [Henry is different. He loves to be doing.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [Henry is different. He LAH1VZ to be DUW1IH0NG.] contains unknown char/phoneme: [H].Original text: [Henry is different. He loves to be doing.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [And if I HHAE1V good luck, your mother SHAE1L have some.] contains unknown char/phoneme: [A].Original text: [And if I have good luck, your mother shall have some.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [And if I HHAE1V good luck, your mother SHAE1L have some.] contains unknown char/phoneme: [I].Original text: [And if I have good luck, your mother shall have some.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [and I BIH0LIY1V there is SKEH1RSLIY0 a YAH1NG LEY1DIY0 in the United Kingdoms.] contains unknown char/phoneme: [I].Original text: [and I believe there is scarcely a young lady in the United Kingdoms.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [and I BIH0LIY1V there is SKEH1RSLIY0 a YAH1NG LEY1DIY0 in the United Kingdoms.] contains unknown char/phoneme: [U].Original text: [and I believe there is scarcely a young lady in the United Kingdoms.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [It is NAA1T AE1T AO1L what I LAY1K, HHIY1 continued.] contains unknown char/phoneme: [I].Original text: [It is not at all what I like, he continued.]. Symbol will be skipped.
[NeMo W 2023-01-31 10:06:18 tts_tokenizers:478] Text: [It is NAA1T AE1T AO1L what I LAY1K, HHIY1 continued.] contains unknown char/phoneme: [I].Original text: [It is not at all what I like, he continued.]. Symbol will be skipped.
```

But it seems that the original text is made up of just some ordinary words. 
Is it normal?
What needs to be done about it?
Thanks!