There are no observations that put the Big Bang into question.  There are  observations that put some of the details in question but this only indicates that the Big Bang is an event that is more complex than our current scientific theories can describe.

It is not correct to state that the Big Bang has no cause.  As yet no cause has been observed but this does not mean there was no cause.  For centuries disease was a mystery until Pasteur used the microscope to observe bacteria and do experiments.  The Big Bang is a theory how the universe evolved once the process started based upon observation and experiment.  People may speculate what caused it but until observations and experiments are done it remains just speculation.  Absence of evidence is not evidence of absence.

One possible observation is related to the concept we know of called cause and effect.  In the natural world, every effect has a cause.  A cause is responsible for an effect.  For example, erosion (an effect) is caused by running water, wind or ice movement.  If the big bang was the beginning of existence for everything in space and time as the theory suggests, there would have been nothing in existence to cause the big bang. If there is no cause, how did we get the effect of the big bang? If there was no universe before the big bang, what was the cause of its creation? Is it possible to have an effect without a cause?  Is the big bang a natural event since it has no apparent cause?

It appears there are more questions than answers about this aspect of the big bang.