PLATFORM_OtaGetOtaInternalPartitionConfig returns internal partition configuration structure, what you could try is make the initialization manually, to ensure the internal flash is selected and the values start at 0.
Let me know if that worked for you.
OtaPartition_t Test_ota_partition =
{
/*start_offset*/ 0,\
/*size*/ 0,\
/*sector_size*/ 0,\
/*page_size*/ 0,\
/*internal_flash*/ true,\
/*spi_baudrate*/ 0,\
};
loader_info.partition_desc = &Test_ota_partition;