Slow queries only on slaves (postgresql) - postgresql

Question

I am using the largest size Postgresql Aurora Cluster.(Engine Version 13.3)
When only the Writer Cluster Endpoint was used, no slow queries occurred at all.
However, when Read Query is modified to use Reader Instance, Slow Query occurs.
(Sometimes queries take more than 10 seconds. And when executed in Writer, it ends in milliseconds, but in Reader, it takes more than 1 second.)
When the exact same Query is executed in the Master, the query is fast. Even if you look at the query plan, Reader and Writer are the same.
Cache hit metrics did not go down in AWS monitoring metrics.
What should be checked to determine the cause and fix it?
Highest Time Node Info
First Query on Master
Node Type Index Scan
Parent Relationship Outer
Parallel Aware true
Scan Direction Forward
Index Name trace_idx09
Schema public
Alias trace_
Startup Cost 0.69
Total Cost 15609.54
Plan Rows 1610
Plan Width 24
Actual Startup Time 5.936
Actual Total Time 50.491
Actual Rows 2902
Actual Loops 3
Rows Removed by Index Recheck 0
Shared Hit Blocks 3917
Shared Read Blocks 396
Shared Dirtied Blocks 0
Shared Written Blocks 0
Local Hit Blocks 0
Local Read Blocks 0
Local Dirtied Blocks 0
Local Written Blocks 0
Temp Read Blocks 0
Temp Written Blocks 0
I/O Read Time 870.529
I/O Write Time 0
Workers [object Object],[object Object]
*Planner Row Estimate Factor 1.8024844720496895
*Planner Row Estimate Direction 1
*Actual Duration 151.473
*Actual Cost 15609.54
*Slowest Node (by duration) false
*Largest Node (by rows) true
*Costiest Node (by cost) true
First Query on Slave
Node Type Index Scan
Parent Relationship Outer
Parallel Aware true
Scan Direction Forward
Index Name trace_idx09
Schema public
Alias trace_
Startup Cost 0.69
Total Cost 15609.54
Plan Rows 1610
Plan Width 24
Actual Startup Time 3046.454
Actual Total Time 3387.273
Actual Rows 2902
Actual Loops 3
Rows Removed by Index Recheck 0
Shared Hit Blocks 1096
Shared Read Blocks 4191
Shared Dirtied Blocks 0
Shared Written Blocks 0
Local Hit Blocks 0
Local Read Blocks 0
Local Dirtied Blocks 0
Local Written Blocks 0
Temp Read Blocks 0
Temp Written Blocks 0
I/O Read Time 8763.617
I/O Write Time 0
Workers [object Object],[object Object]
*Planner Row Estimate Factor 1.8024844720496895
*Planner Row Estimate Direction 1
*Actual Duration 10161.819
*Actual Cost 15609.54
*Slowest Node (by duration) true
*Largest Node (by rows) true
*Costiest Node (by cost) true
Second Query on Slave
Node Type Index Scan
Parent Relationship Outer
Parallel Aware true
Scan Direction Forward
Index Name trace_idx09
Schema public
Alias trace_
Startup Cost 0.69
Total Cost 15609.54
Plan Rows 1610
Plan Width 24
Actual Startup Time 3.734
Actual Total Time 8.375
Actual Rows 2902
Actual Loops 3
Rows Removed by Index Recheck 0
Shared Hit Blocks 4039
Shared Read Blocks 2
Shared Dirtied Blocks 0
Shared Written Blocks 0
Local Hit Blocks 0
Local Read Blocks 0
Local Dirtied Blocks 0
Local Written Blocks 0
Temp Read Blocks 0
Temp Written Blocks 0
I/O Read Time 3.538
I/O Write Time 0
Workers [object Object],[object Object]
*Planner Row Estimate Factor 1.8024844720496895
*Planner Row Estimate Direction 1
*Actual Duration 25.125
*Actual Cost 15609.54
*Slowest Node (by duration) false
*Largest Node (by rows) true
*Costiest Node (by cost) true