Facing read/write timeout in the middle of Cassandra rolling upgrade from Cassandra 3.0.15 to 4.1.4

Im preparing to upgrade my Cassandra cluster (3 Nodes x 2 DCs) from Cassandra 3.0.15 to 4.1.4, when i tried the upgradation process in a similar setup i faced following issues in the middle of the rolling upgrade. **0) Schema version mismatch:** Cluster status --> DC1 : ( 1 x 4.1.4 ) + ( 2 x 3.0.15 ) && DC2 : 3 x 3.0.15 Schema versions: (Its not an issue) 77876dfb-de1f-3826-89b2-ff6d502bcd6c: [C* 3.0.15 node ips] 018b628e-98aa-36f4-9e7e-a40cca8bc44d: [C* 4.1.4 node ip] ***1) ReadTimeoutException from client*** Cluster status --> DC1 : ( 1 x 4.1.4 ) + ( 2 x 3.0.15 ) && DC2 : 3 x 3.0.15 Caused by: com.datastax.driver.core.exceptions.ReadTimeoutException: Cassandra timeout during read query at consistency LOCAL_QUORUM (2 responses were required but only 1 replica responded) Above issue happened when i tried query configuring Cassandra 4.1.4 node as the coordinator node. Query succeeded only after reduced the consistency to LOCAL_ONE. **Things worked smoothly when all the nodes are Cassandra 3.0.15, so there is no network latency.** **2) ReadTimeout from CQLSH** Cluster status --> DC1 : ( 1 x 4.1.4 ) + ( 2 x 3.0.15 ) && DC2 : 3 x 3.0.15 ReadTimeout: Error from server: code=1200 [Coordinator node timed out waiting for replica nodes' responses] message="Operation timed out - received only 0 responses." info={'consistency': 'ONE', 'required_responses': 1, 'received_responses': 0} Inconsistently getting above exception when executing query from in the CQL SHELL of the nodes of the DC with mixed versions of Cassandra. > ***Note :*** I tried query(SELECT *) a table which has replication factor of 2 via CQL SHELL of each node, I observed that I'm getting > above exception from Cassandra 3.0.15 nodes alone not from Cassandra > 4.1.4 node. **3) UnauthorizedException** Cluster status --> DC1 : ( 1 x 4.1.4 ) + ( 2 x 3.0.15 ) && DC2 : 3 x 3.0.15 Caused by: com.datastax.driver.core.exceptions.UnauthorizedException: Unable to perform authorization of super-user permission: Operation timed out - received only 1 responses.