Symptom: ArchivesSpace crashes with out of memory errors. Indexer held up on events.
I haven't looked into the underlying factors but we've found that (at least from) transferring records between repositories that duplicate event relationships can be created. If the transferred record is particularly "large" there can be thousands of duplicate event relationships which will crash the indexer as it attempts to retrieve and resolve them.
I created this plugin to delete the duplicate event relationships: