"initWebApplicationContext Context initialization failed" after attempt to run Confluence 5.5.7

Trying to test my plugin for an older version of Confluence (5.5.7), I’m failing to get Confluence to start up ever since by running atlas-run.

The log suggests that this one is the initial error/exception:

[INFO] [talledLocalContainer] 2020-07-31 10:34:38,125 ERROR [localhost-startStop-1] [springframework.web.context.ContextLoader] initWebApplicationContext Context initialization failed

[INFO] [talledLocalContainer] org.springframework.beans.factory.BeanCreationException:
Error creating bean with name '__registration_bean':
Invocation of init method failed;
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'referralTaskQueue' defined in class path resource [applicationContext.xml]:
Cannot resolve reference to bean 'referralManager' while setting bean property 'referralManager';
nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'referralManager' defined in class path resource [applicationContext.xml]:
Cannot resolve reference to bean 'settingsManager' while setting bean property 'settingsManager';
	nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'settingsManager' defined in class path resource [applicationContext.xml]:
	Cannot resolve reference to bean 'upgradeManager' while setting bean property 'upgradeManager';
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'upgradeManager' defined in class path resource [upgradeSubsystemContext.xml]:
Cannot resolve reference to bean 'personalSpaceCreatorCheckUpgradeTask' while setting bean property 'upgradeTasks' with key [20];
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'personalSpaceCreatorCheckUpgradeTask' defined in class path resource [upgradeSubsystemContext.xml]:
Cannot resolve reference to bean 'userAccessor' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'userAccessor' defined in class path resource [applicationContext.xml]:
Cannot resolve reference to bean 'userAccessorTarget' while setting bean property 'target';
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'userAccessorTarget' defined in class path resource [applicationContext.xml]:
Cannot resolve reference to bean 'repositoryAccessor' while setting constructor argument;
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'repositoryAccessor' defined in class path resource [atlassianUserContext.xml]:
Cannot resolve reference to bean 'userManager' while setting bean property 'userManager';
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'userManager' defined in class path resource [atlassianUserContext.xml]:
Cannot resolve reference to bean 'backingUserManager' while setting constructor argument;
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'backingUserManager' defined in class path resource [atlassianUserContext.xml]:
Cannot resolve reference to bean 'crowdService' while setting constructor argument; nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'crowdService' defined in class path resource [importedEmbeddedCrowdContext.xml]:
Cannot resolve reference to bean 'crowdServiceTarget' while setting bean property 'target';
	nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'crowdServiceTarget':
FactoryBean threw exception on object creation; nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'unfilteredCrowdServiceTarget' defined in class path resource [importedEmbeddedCrowdContext.xml]:
Cannot resolve reference to bean 'crowdApplicationService' while setting constructor argument;
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'crowdApplicationService' defined in class path resource [importedEmbeddedCrowdContext.xml]:
Cannot resolve reference to bean 'crowdDirectoryManager' while setting constructor argument;
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'crowdDirectoryManager' defined in class path resource [importedEmbeddedCrowdContext.xml]:
Cannot resolve reference to bean 'directoryInstanceLoader' while setting constructor argument;
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'directoryInstanceLoader' defined in class path resource [importedEmbeddedCrowdContext.xml]:
Cannot resolve reference to bean 'crowdInternalDirectoryLoader' while setting constructor argument with key [0];
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'crowdInternalDirectoryLoader' defined in class path resource [importedEmbeddedCrowdContext.xml]:
Cannot resolve reference to bean 'instanceFactory' while setting constructor argument;
	nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'instanceFactory' defined in class path resource [embeddedCrowdContext.xml]:
Invocation of init method failed; nested exception is java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Class

[...]

I tried to find my way around other similar reports, but so far didn’t find any hint which seemed to apply to my case.

What I did when this error first occurred:
Previously I simply started Confluence by running atlas-run on the source tree. That started Confluence 5.10.x and all worked fine.
I then wanted to test the application against Confluence 5.5.7 and ran: atlas-run --product confluence --version 5.5.7 (without a prior call of atlas-clean).
Ever since this just failed to start up.

I tried multiple commands in-between meanwhile (including atlas-clean and just starting atlas-run again) but always end up with the error.

Any pointers what’s going on here?

Seems like this exception is unrelated to the problem which caused my plugin to fail (which I’ve fixed now). Still, I’d like to fix this exception or at least understand why it suddenly started occurring, if possible.