There seems to be database contention between 16:10 and midnight UTC on the 26th of june:
https://logstash.wikimedia.org/goto/3bcfe493d8d19739bca928d1b413d4e9
Several MessageGroupStats-related errors (such as Wikimedia\Rdbms\DatabaseMysqlBase::lock failed to acquire lock 'MessageGroupStats:updates' seems to be happening on meta and mediawiki.org at that time. While in commonly used database rows that would point to an overload, on less commonly used functions, that would normally point to a bug.
Potentially related to T53410