This issue is well known and related to lack of ENC coverage. A small part in the southern part of the Strait of Formosa is only covered by the cell KR1M0000. This cell are in compilation scale 1: 2 000 000 and has les details than the surrounding cells in compilation 1 : 250 000. There is nothing we can do with this and hope soon UKHO can implement a better coverage in the AVCS database.