db1077 is definitely having BBU issues (T225391 - T225391#5261662) and db1077 servers production traffic on s3 (and it is also sanitarium master)
db1112 is now serving on the test cluster as a replica.
This set of hosts have minimal traffic (https://grafana.wikimedia.org/d/000000273/mysql?orgId=1&var-dc=eqiad%20prometheus%2Fops&var-server=db1112&var-port=9104&from=now-6M&to=now), so there should be no performance issues with db1077 there without a BBU as a test-cluster slave.
The idea is to exchange db1077 with db1112 so we can have db1112 serving in production and acting as sanitarium master as it has a healthy BBU