I think we'd better try to determine why the index is unavailable before doing what's done in your PR (i.e. ignoring the error).
Could you please provide more information about your error? A failing test case would be the best: you may find a template here.

If you cannot provide a test case, maybe you have the full error log available, especially with the startup logs? I'm wondering what happened for the index to be reported missing.

Also, what configuration are you using? Did you set hibernate.search.default.elasticsearch.index_schema_management_strategy (or the equivalent for indexa or indexb) to something other than the default?