XDCR Diff Tool Occasionally Stuck – Processing Rate Drops to Zero

We've observed an intermittent issue where the XDCR diff tool gets stuck during execution. The behavior is inconsistent—after re-running the diff, the issue typically resolves itself without any changes to the environment or script.

Symptoms:

• The target process appears to be stuck.
• Processing rate drops to 0 mutations/second, even though mutations are present.
• Example logs:

2025-08-08T08:02:08.749Z INFO GOXDCR.xdcrDiffTool: target processed 115812508 mutations, filtered 0 mutations, 0 failed filtering. processing rate=0 mutation/second
2025-08-08T08:02:13.749Z INFO GOXDCR.xdcrDiffTool: target processed 115812508 mutations, filtered 0 mutations, 0 failed filtering. processing rate=0 mutation/second
2025-08-08T08:02:18.749Z INFO GOXDCR.xdcrDiffTool: target processed 115812508 mutations, filtered 0 mutations, 0 failed filtering. processing rate=0 mutation/second

Questions:

• What might be causing the XDCR diff tool to get stuck?
• Why does the issue resolve itself after a re-run?
• How can we prevent this from happening in future executions?

No source files or tests are named. Start by reproducing an XDCR diff run and compare the processing logs when the target stalls with a successful re-run, focusing on the unchanged processed-mutation count and zero rate. Done means the stall's cause is identified and a prevention or recovery change is verified against the observed behavior.