Bootstrap with juju 2.7.8. Deploy mysql and Wordpress, add relation between them. Once settled, upgrade the controller then the model to 2.9.4. The Wordpress unit goes into an error state because the install hook failed.
unit-wordpress-0: 21:22:03 INFO juju.worker.uniter.operation ran "install" hook
unit-wordpress-0: 21:22:25 INFO juju.worker.uniter.operation ran "start" hook
unit-wordpress-0: 21:22:57 INFO juju.worker.uniter.operation ran "db-relation-changed" hook
machine-4: 21:25:21 INFO juju.cmd running jujud [2.9.5.1 0 gc go1.14.15]
machine-4: 21:25:24 INFO juju.worker.upgradesteps upgrade to 2.9.4 completed successfully.
unit-wordpress-0: 21:25:26 INFO juju.worker.uniter found queued "install" hook
unit-wordpress-0: 21:25:30 ERROR juju.worker.uniter.operation hook "install" (via explicit, bespoke hook script) failed: exit status 128
Does not occur upgrading from 2.7.8 to 2.8.11, nor from 2.8.10 to 2.9.4
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