If +/- 95% confidence interval includes 1, statistical significance is ruled out. However, you may notice such an interval (1.00 to 2.43) that is indeed statistically significant. This might happen in case that only two significant digits are given, rounding an interval that is, let's say, 1.003 to 2.427.

This is entirely possible, but it theoretically depends on the level of precision of the estimate (e.g., 1.000, 1.001, 1.0001, etc.). In the case of the paper that you read which reports a 95% CI of 1.00 to 2.43 as statistically significant, I agree with what Vasileios Papadopoulos said that may have led to a p-value of < 0.05 (meaning that 1.000000... was not crossed, mathematically speaking).

However, take note that statistical significant IS NOT clinical significance. Given that information from the paper and the authors" interpretation of it, you have to decide for your own on whether the "statistically significant" association is indeed relevant or artefactual.

What is your outcome? You act like it is a ratio of some sort but don't state it. You can have confidence intervals for any measure, including ratios and non-ratios.

I second the answers of Aedrian Abrilla and Vasileios Papadopoulos . It depends on the research questions and precision of the estimate. As most of the journals allow upto 2 decimal significant digits, it might be possible that 1 was crossed but at third or fourth decimal point so authors ignored. Secondly, based on your research question, you have decide which one will you consider to make an interpretation, either 95% CI or P-value. Although it is recommended to interpret your results based on 95% CI rather than simple p-value. Peers might elaborate it further.