The reason

The reason that I don’t like coffee is that it tastes bitter.
Is this correct? If not then what kind of correction should be made?

Can I finish just by “a full stop” at the bold part?

Yes, it’s OK. The repetition of “that” is faintly awkward when seen written down, and could be avoided by omitting the first “that”.

“If not then what kind of correction should be made?” is a question and requires a question mark.

I am told that in indirect question there is not require of question mark. But I forgot the patter of an indirect question. Could you please give me a example of indirect question where there is no require of question mark.

The reason that I don’t like coffee is it tastes bitter.
Is it correct?

Dozy answered that in message #2.

Dozy suggested me to eliminate that first “that” to resolved awkwardness. But I eliminated the second “that”.
Does it remove awkwardness?

I think it is better to say like this:
The reason that I don’t like coffee because its taste is bitter.
Bitter is an adjective to coffee and it must precede by a verb.

I think this is ungrammatical.

You are right.
an ‘is’ is missing.

… is because its taste is bitter.

Dozy suggested me to eliminate the first “that” to resolved awkwardness. But if I omit the second “that” then does it remove awkwardness?

Yes, that’s OK too.

You could also remove both instances of ‘that’:
The reason I don’t like coffee is it tastes bitter.

(However my preference would be Dozy’s suggestion.)

Choose the correct answer.
a. The reason that I don’t like coffee is that it tastes bitter.
b. The reason that I don’t like coffee is because it taste bitter.
c. The reason I don’t like coffee is because it tastes bitter.
d. The reason I don’t like coffee is that it tastes bitter.

Is the above question flawed?

They are all correct assuming that the word ‘taste’ in (2) is a typo for ‘tastes’.

The reason I don’t like coffee is because it tastes bitter.
Some people say that since “The reason” already mentioned so “because” is redundant here.
Dozy/Bev,
I would like to get a comment from anyone of you two.

Is this correct sentence?

'Just like ‘that’ (discussed above), ‘because’ can be included or omitted. Both are equally acceptable.

You need to use ‘any one’ rather than ‘anyone’ there as you mean either of the two of us.

The reason because I don’t like coffee is because it tastes bitter.
What about now?

No, that doesn’t work.
‘The reason because’ is grammatically incorrect.

My quote does not mean that ‘because’ can be used instead of ‘that’. It means that in your second example ‘because’ follows the same principle as ‘that’ followed in your first example. The two words are not interchangeable.