According to the docs,
the X-Ray SDK applies a sampling algorithm to determine which requests get traced. By default, the X-Ray SDK records the first request each second, and five percent of any additional requests.
Is it possible to trace all requests?
It is possible to set the sampling rate to 100%.
However, as noted in the FAQs:
X-Ray should not be used as an audit or compliance tool because it does not guarantee data completeness.