Explanation of the error:
This Salesforce validation error that Gearset is surfacing is likely to occur on the Asset component of CustomObject metadata type:
ControlledByParent is not a valid sharing model for Asset
In the use case we've investigated, user tried to deploy changes from one Salesforce org to another. In that particular scenario we looked at user claimed the Sharing Rules were supposedly identical between the two orgs.
Resolution:
Workaround that helped with resolving this error was to change the Asset Sharing Settings in the target org from "Controlled by Parent" to "Public Read Only".
In your Salesforce org you can find this setting in Security > Sharing Settings > Edit:
This allowed the deployment to happen without that error.
For guidance on how to amend Asset Settings check Salesforce documentation:
Configure Asset Settings, and
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More information on a possible resolution to this error can be found here:
Salesforce StackExchange
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Disclaimer: This error is returned by Salesforce directly, rather than Gearset. Even so, we offer guidance based on our combined experience with the Metadata API. Where possible, we try to help guide you to fix or avoid this error. In the case that this isn't possible, we may need to direct you to Salesforce support for further clarification.