Notice: I tried to submit a bug report but because there is no crash dumb and the form prevents submission without attachment, and also prevents me from submitting replacements I post this here.
Persistent structure error, and still appears in 5.7.3 first reported here Unreal Engine 5.6 Released - #119 by unit23
Steps to reproduce: Use the build-in BuildTool, which pops up when i.e. adding an outdated plugin to the plugin folder - used Strider which was maintained until 5.4, and since has been removed from FAB. Building manual (explained here Compiling a plugin for a new engine version | Community tutorial) fails. However, the auto BuildTool popup which appears on editor launch successfully builds the plugin.
Subsequently, building the project with Strider code fails with unknown structure error. Removing the plugin and related code still results in the unknown structure error. Same after deleting intermediate, Save and DerivedDataCache. But, can be resolved by selecting related blueprint content such as the AnimGraph and using the refresh feature.
The current auto build tool is successfully building plugins even with errors.