Following group1 promotion to 1.38.0-wmf.17 there was a large spike in read-only related errors and slow queries. Unfortunately I wasn't able to select a specific relevant root error to report, but it appears that many of the slow queries are related to INSERTs made to the pagelinks and templatelinks tables, suggesting a possible relation to the risky patch in T293958#7612230
See the slow queries logstash dashboard here as well as exceptions around the same time window as today's group1 rollout.
https://logstash.wikimedia.org/goto/fc93968e03e382d6ead41535bab7133f