txn throw exception Region epoch not match after retries

./pd-server --version
Release Version: v4.0.0-rc.2-563-gaa22efb5-dirty
Edition: Community
Git Commit Hash: aa22efb50906e2d0fb1306bd2af6813969e46d73
Git Branch: master
UTC Build Time: 2021-05-27 04:38:59

Release Version: 5.1.0-alpha
Edition: Community
Git Commit Hash: cd905a208293c2b0c1fca9aa2756d5c26392b38c
Git Commit Branch: master
UTC Build Time: 2021-05-28 09:25:25
Rust Version: rustc 1.53.0-nightly (16bf626a3 2021-04-14)
Enable Features: jemalloc mem-profiling portable sse protobuf-codec test-engines-rocksdb cloud-aws cloud-gcp
Profile: release

src:
count=1000000
Txn txn(test_cluster.get());

try{
    char keyName[32];
    std::string keyValue( 512, 'x');

    auto begin_tm = timeSinceEpochMillisec();
    for( int i = 1;i<=count;i++){
        sprintf(keyName, "c%d", i);
        txn.set(keyName, keyValue);
    }
    txn.commit();
    auto end_tm = timeSinceEpochMillisec();
    printf("time:%ld\n", end_tm- begin_tm);
}
catch ( Exception & e) {
    std::cerr << "exception caught: " << e.displayText() << '\n';
}

[19:42:06] [(0)] Information: load store id 2001 address 172.16.16.21:20160
[19:43:33] [(0)] Warning: region {44103,3,29} find error: EpochNotMatch current epoch of region 44103 is conf_ver: 3 version: 30
[19:43:33] [(0)] Information: region stale for region {44103,3,29}.
[19:43:33] [(0)] Information: try drop region {44103,3,29}
[19:43:33] [(0)] Information: drop region 44103 because of send failure
[19:43:33] [(0)] Warning: region {44127,3,30} find error: peer is not leader for region 44127, leader may None
[19:43:33] [(0)] Information: report not leader but doesn't have new leader
[19:43:33] [(0)] Information: try drop region {44127,3,30}
[19:43:33] [(0)] Information: drop region 44127 because of send failure
[19:43:53] [(0)] Warning: write commit exception: Exception: Region epoch not match after retries: Region {44103,3,29} not in region cache.
exception caught: Exception: Region epoch not match after retries: Region {44103,3,29} not in region cache.

Start by reproducing the C++ transaction shown in the report and trace txn.commit through its region-cache retry handling, using the EpochNotMatch and not-leader log messages as checkpoints. Done means the reported workload no longer throws “Region epoch not match after retries,” with a regression test covering the retry scenario; the report names no source files or existing tests.