I have two doris environments that:
A: Centos7.8
B: Centos7.5

The table like this:
create table table1
(
dept_id int ,
user_id bitmap bitmap_union
)
AGGREGATE KEY(dept_id)
DISTRIBUTED BY HASH(dept_id) BUCKETS 1
PROPERTIES("replication_num" = "1");

environment A:

insert into table1 values (1,to_bitmap(1001));
select bitmap_count(bitmap_union(user_id)) from table1;
--output is 1， No problem。
insert into table1 values (1,to_bitmap(1002));
select bitmap_count(bitmap_union(user_id)) from table1;
--output is 2， No problem too。

environment B:

insert into table1 values (1,to_bitmap(1001));
select bitmap_count(bitmap_union(user_id)) from table1;
--output is 1， No problem。
insert into table1 values (1,to_bitmap(1002));
select bitmap_count(bitmap_union(user_id)) from table1;
--Now ,I get one error mesage is:
ERROR 2013 (HY000): Lost connection to MySQL server during query

at the same time, BE crashed.
then I check the log,I find the failed mesage like this :
alpha_rowset.cpp:178] failed to get largest_segment_group. is null: 1. version: 3-3. tablet: 10007