[next gen on clould] workload can not balance after tidb auto scale out

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1、Increase workload pressure
2、tidb auto scale out from 6 to 12

2. What did you expect to see? (Required)

workload can balance after tidb auto scale out

3. What did you see instead (Required)

workload can not balance after tidb auto scale out

4. What is your version? (Required)

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| Release Version: v9.0.0-beta.2.pre-379-g11cddd5
Edition: Enterprise
Git Commit Hash: 11cddd586ab233f87868b450532ff06a3f3c660f
Git Branch: HEAD
UTC Build Time: 2025-08-23 02:55:18
GoVersion: go1.23.12
Race Enabled: false
Check Table Before Drop: false
Store: tikv
Enterprise Extension Commit Hash: dc633aae52eb11b4e3549e3a7ef5b0ed14e159b1
Kernel Type: Next Generation |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.002 sec)

MySQL [(none)]>

tiproxy version
version: 8.0.11-TiDB-v9.0.0-beta.2.pre-344-ga657e4d