Replicated the bug on 7.1.3-3480. Seeing a similar stack trace and seeing  panic: 

goxdcr.log: /home/couchbase/.cbdepscache/exploded/x86_64/go-1.18.7/go/src/runtime/panic.go:992 +0x71 fp=0xc0003bf3a0 sp=0xc0003bf370 pc=0x43a891

The UI hangs and becomes unusable. I am unable to list or create replications from the UI and REST. REST throws an unexpected server error: ["Unexpected server error, request logged."]

Validated the fix for this issue on 7.1.4-3585. Not seeing panics in logs or hangs in UI.

Reproduction steps originally posted in the original MB: https://couchbasecloud.atlassian.net/browse/MB-55354?focusedCommentId=845008&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel

May require adding injection if system load is not high enough to induce delay
https://review.couchbase.org/c/goxdcr/+/186009
Specifically, replication setting xdcrDevBackfillReplUpdateDelayMs
Test case: https://review.couchbase.org/c/goxdcr/+/186009/3/tools/testScripts/collectionTestcases/4k_explicit_mapping_change_w_delay.shlib

= Can you please help with steps to validate.

Build couchbase-server-7.1.4-3584 contains goxdcr commit 4f10009 with commit message:
: reproduction test case and injection needed to hit

Build couchbase-server-7.1.4-3584 contains goxdcr commit 8caede0 with commit message:
: Fix and unit test for backfill manager and pipelineMgr deadlock