Why am I unable to Left Join two tables?

Question

This is the query that I have performed.

select *
from samples
left join ETL_freemark on samples.lab_number_code=ETL_freemark.Lab_Number;

Both tables have only about 1,000,000 rows in it. 'Samples' table is able to left join easily with other tables.

It is only when it is left joined to 'ETL_freemark' that is returning with the

Error Code: 2013. Lost connection to MySQL server during query 30.016 sec

After increasing DBMS connection keep-alive interval/read timeout/connection timeout to 3000 seconds and making indexes for samples.lab_number_code and for ETL_freemark_Lab_number this error comes out instead

Error Code: 1105. The last transaction was aborted due to Seamless Scaling. Please retry. 44.266 sec"

And these 3 queries work fine.

select *
from samples

and

select *
from ETL_freemark

and

select *
from samples
inner join ETL_freemark on samples.lab_number_code=ETL_freemark.lab_number

Using explain select results are these:

explain select *
        from samples
        left join ETL_freemark on samples.lab_number_code=ETL_freemark.Lab_Number;

1   SIMPLE  samples             ALL                 132440  100.00  
1   SIMPLE  ETL_freemark        ALL                 179093  100.00  Using where; Using join buffer (Block Nested Loop)

Any ideas on why my left join is not working?