ReportPortal database becomes unstable and reporting almost fully stops except for small launches with approximately 1 test inside when the test_item.path field is exceeded the allowable "ltree" field type indexing limit (path length>=120 approximately, recursive nesting of the nested steps).
REINDEX INDEX path_gist_idx and path_idx aren't helped.
Patches
The problem was fixed in service-api module of version 5.10.0 (product release 23.2), where the maximum number of nested elements were programmatically limited.
Workarounds
After deletion of the data with long paths, and reindexing both indexes (path_gist_idx and path_idx), the database becomes stable and ReportPortal is working properly.