Build couchbase-server-7.2.0-5000 contains indexing commit 6f1729a with commit message:
: indexer blocked during storage warmup on MOI storage, causing rebalance failure.

Closing this based on dev-verification. Steps to repro are mentioned in the above comment

Build couchbase-server-7.1.2-3321 contains indexing commit 6f1729a with commit message:
: indexer blocked during storage warmup on MOI storage, causing rebalance failure.

Validated the fix using the following steps:

a. Add a sleep of 100 seconds in MemDBSlice::OpenSnapshot method

b. Populate 10k documents in the bucket default

c. create index idx_1 on default(name)

d. Failover indexer node after index build is finished

e. Add back the indexer node and initiate rebalance

Before the fix: Rebalance failed with timeout on "PrepareTopologyChange" message

After the fix: Prepare phase goes through and ns_server sends a StartTopologyChange. Rebalance master waits for 10 minutes for indexer to warmup i.e. load the snapshot