The actual ground track orbit of the Sentinel-3B (S3B) satellite has been observed to violate the nominal dead-band of +/- 1km from the reference orbit over different periods of the year 2023 as you can see from the figure here below.
The left axis of the plot corresponds to the maximum ground track deviation w.r.t. the S3B reference orbit +only if > -1 km (so violating the dead-band), when the right axis corresponds to the latitude for those violations.
In the case of S3B, the dead-band violations occur over every latitude band, and quite frequently in August 2023 when crossing the equator.
Users are informed that this issue may impact the performance of the S3B Altimetry Inland Water data products.
The joint ESA-EUMETSAT Sentinel-3 project is working to ensure a better maintenance of the S3B satellite unit within the nominal dead-band.