ISSUE DESCRIPTION AND IMPACT
In MongoDB version 6.0.17, some large aggregation pipelines may return incorrect results, cause a mongod or mongos to crash, or raise an error when it did not previously. Affected aggregation pipelines are those that:

• Exceed 30,000 bytes in size, and
• Contain at least one $group and/or $lookup stage near the beginning of the pipeline, potentially preceded by a $match, $project, $addFields or $sort stage

Affected operations may omit one or more $group or $lookup stages in the aggregation pipeline, resulting in operations that return incorrect results or generate errors.

DIAGNOSIS AND AFFECTED VERSIONS
MongoDB Server version 6.0.17 is subject to the bug. No other versions are affected.

REMEDIATION AND WORKAROUNDS
Customers are advised to:

• Upgrade to 6.0.18, or
• Customers staying on 6.0.17 should set the internalQueryForceClassicEngine parameter to true with the following command:
  db.adminCommand({setParameter: 1, internalQueryForceClassicEngine: true})