Currently, transactions are sorted by timestamp, then order. This sometimes leads to case when transaction included in higher block is returned next to the transaction included in lower block. Because timestamp of two blocks are the same. This only may happen in testnet in real world, but we still should sort by block height first

Example:
https://chain.so/api/v2/block/BTCTEST/00000000000040b0a1862451e646fc5ab82c54881e7d9746e6571d4a77600449
https://chain.so/api/v2/block/BTCTEST/00000000000078957dd7143156e4d577304a9dc4eaf88fb5de7987a4f18807e2