In the early stages of pregnancy it is very easy to get positive and negative results with different samples of urine, at different times of day and with different tests. For me in early pregnancy I always got a better result with second morning urine rather than first! Even the amount of ink in the same batch of tests can vary. So testing the same urine sample with the same type of test can yield different results. So early testing is very irratic.
However, the test you posted a picture of is not faint by any means, and that is what makes me wonder if the test was not correct.
I have had 15 pregnancies and all but the first I tested early and followed through the testing til miscarriage or 12 week scan! So I do have a bit of experience of this. The strength of the result from the test you posted in your OP, would not just disappear to a very faint result the following day, except if the urine you used the second day was very dilute and the previous day very strong.
Were the CB tests digital or normal tests? Digital tests are generally less sensitive, so them being negative would not surprise me if it is early, but with the strength of response to the first test, it should have even turned a digital test positive if using the same urine sample. Did you used the same sample for both tests done yesterday and the tests this morning were they both done in the same sample or separately?
I am now a little confused you said in your OP that the test today was a BFN, but now you are saying it was a faint positive. Can you post pictures of the other tests?