unique key hash分桶数据倾斜

doris2.1.9使用UNIQUE KEY Id bigint NOT NULL作为分桶键DISTRIBUTED BY HASH(Id) BUCKETS 8，仍然产生了数据倾斜的情况
"BucketIdx","AvgRowCount","AvgDataSize","Graph","Percent"
"0","39470","3485395",>>>>>>>>>>>>>>>>,"16.88 %"
"1","30235","2690570",>>>>>>>>>>>>>,"13.03 %"
"2","29866","2658435",>>>>>>>>>>>>,"12.87 %"
"3","25049","2237446",>>>>>>>>>>,"10.84 %"
"4","26317","2349757",>>>>>>>>>>>,"11.38 %"
"5","28558","2545532",>>>>>>>>>>>>,"12.33 %"
"6","28685","2542321",>>>>>>>>>>>>,"12.31 %"
"7","24129","2140665",>>>>>>>>>>,"10.37 %"

上官网查询到分桶策略
Hash 分桶：通过计算分桶列值的 crc32 哈希值，并对分桶数取模，将数据行均匀分布到分片中。
于是我使用 crc32(id)%8 发现其数据应该是分布均匀的，
"bucket_no","count(1)"
0,9549
1,9601
2,9486
3,9518
4,9452
5,9488
6,9567
7,9573
为什么会出现这种情况，是BUG吗？