SonarQube Community Build 26.6 upgrade from 25.12 fails with "Please upgrade to the 25.12 version fi

Environment:
- Current version: SonarQube Community Build 25.12.0.117093
- Target version: SonarQube Community Build 26.6.0.123539
- Database: PostgreSQL 14.23
- Java: OpenJDK 21.0.11
- OS: Ubuntu 22.04

Issue:
Attempting to upgrade from SonarQube Community Build 25.12.0.117093 to 26.6.0.123539 results in startup failure:

"The version of SonarQube you are trying to upgrade from is too old. Please upgrade to the 25.12 version first."

Observations:
- Current 25.12 instance is healthy and operational.
- API confirms version:
  curl http://localhost:9000/api/server/version
  returns 25.12.0.117093

Database checks:
- internal_properties.installation.version = 25.12.0.117093
- migration_logs only contain successful migrations for target_version=25.12.0.117093
- schema_migrations maximum version is 202506026
- No failed migration_logs exist.

Upgrade attempts:
- Fresh extraction of 26.6 distribution.
- Copied only sonar.properties.
- Deleted temp/, logs/, and data/es8/.
- Verified Java 21.
- Correct ownership assigned to sonar user.

Despite this, startup fails during DatabaseServerCompatibility validation.

Has anyone successfully upgraded Community Build 25.12 → 26.6?
Is there an additional migration baseline requirement not documented?

Hello @abbasnida and welcome to the Community! There is a known bug (even mentioned in our docs!) which affects some users in this precise way you’re describing. The solution typically is to upgrade to 26.1 first, and then to 26.6. Normally this wouldn’t be required, it’s an exception because of this bug. Could you give it a go?