According to the Flink 1.5 release docs multiple slots per task manager are "not fully supported yet". Can you provide more information about what are the risks of running more than one slot per tm?
We are running Flink on EMR on YARN. Previously we run 4 task task managers with 8 slot each now we are running 32 with 1 slot each. However, since we upgraded to Flink 1.5 we started seeing timeouts taking a connection from AWS S3 SDK pool etc.