HDFS introduced below feature to stop users from creating a file that ends with "." on ABFS:
As a result of this change, Impala now writes to ABFS fails with such error.
I can see that it generates temp file using this format "$0.$1.$2":
$2 is the file extension and will be empty if it is TEXT file format:
HADOOP-15860 was backported into CDH6.2, it is currently only affecting 6.2 and works in older versions.
There is no way to override this empty file extension so no workaround is possible, unless user choose another file format.