KV made the change to restrict DCP feed name length to 200 characters in 7.0.0: https://issues.couchbase.com/browse/MB-34280
This change was picked up by Eventing in 7.0.0 as well: https://issues.couchbase.com/browse/MB-42968 (Your glorious ticket back in 2020)
Kv team then backported this DCP change to 6.6.5: https://issues.couchbase.com/browse/MB-49271
However, Eventing team was not aware of this change in 6.6.5 made by kv. This breaks Rebalance Operation in v6.6.5 when there are usually >~3 nodes in the cluster with Eventing function deployed at the same time.
We do not see this issue with 6.6.4(both kv,eventing did not make the DCP length change) and 7.0.x(both kv, eventing made the DCP length change).
With 6.6.5: kv made the DCP length change, Eventing did not.
Why did we not see this issue with 2.2.x: Because 6.6.5 was released unofficially in January and officially in early March this year(2022): https://issues.couchbase.com/browse/MB-47673
The Eventing change is coming in 6.6.6(no idea about the timeline): https://issues.couchbase.com/browse/MB-51435