2.1.0-rc2: Can't DROP INDEX `data_index_XXX_idx_tree_u1`

I’ve a S3 storage named ovhc (it’s one of two roots that are used for a multi-paths workspace).

During startup I can see the following line:
2020-06-26T13:35:48.658Z ERROR pydio.grpc.data.index.ovhc Failed to init DB provider {"error": "Error 1091: Can't DROP INDEX data_index_ovhc_idx_tree_u1; check that it exists handling data_index_ovhc_idx_0.4.sql"}

I didn’t find actual problem yet, but since it’s an error, I prefer mention it here anyway.