changefeed resolvedTs lag increase after pausing to write data upstream

[wk989898]

What did you do?

1. start a changefeed with mysql
2. write data upstream
3. start 50 changefeed with blackhole
4. pause to write data upstream

What did you expect to see?

No response

What did you see instead?

The changefeed resovledTs lag increase.
The sink writes zero bytes, which means all data should be replicated to the downstream.

Versions of the cluster

Upstream TiDB cluster version (execute SELECT tidb_version(); in a MySQL client):

(paste TiDB cluster version here)

Upstream TiKV version (execute tikv-server --version):

(paste TiKV version here)

TiCDC version (execute cdc version):

release-8.5