HashJoin Anomaly when joining outputs of two Python UDFs

I have two Python UDFs, their columns are: 1st one:

total_mortality_RR_2020	state	state_num
double	string	number

2nd one:

total_mortality_RR_2019	state	state_num
double	string	number

Before I connected them to the HashJoin, their outputs are:

After I connected them directly to the HashJoin(inner join on state_num of integer type):

the tuple mapping is 0 -> 0 for the HashJoin operator, and one of the PythonUDF tuple mapping becomes 50->25 instead of 50->50.

And if I introduced two type-cast operators, convert the state_num column from type integer to string

the HashJoin has the pair 50->0

When changing the join type from inner join to full outerjoin, the pair becomes 50->50, but the result is not correct:

Texera / texera