I do not know what is the current logic, but data loading for a DICOM study loaded from a bucket can be very sluggish - this one below takes minutes:
https://volview.kitware.app/?urls=[s3://idc-open-data/ed38c404-6a39-4d06-9484-86204e81f0b9,s3://idc-open-data/fbac83a8-ea0a-40a2-b415-5cbd0118dc3e,s3://idc-open-data/dd0ac33e-a435-4eaa-9f15-ee7ff4d86ee6,s3://idc-open-data/acde3185-defa-4204-9edc-702978604433,s3://idc-open-data/1714b9de-3a93-4f89-82b5-d3b5724410a2,s3://idc-open-data/4a4ee5ac-6e53-47f4-86cf-63536d4a3be0,s3://idc-open-data/1998d15b-17a2-4e7e-ad29-3cd2b9b70fab,s3://idc-open-data/d9bc4f80-67c6-40de-bf0d-7ca694df131d,s3://idc-open-data/16f94d2a-c3b6-40b2-844a-1df4bcc0dfe1,s3://idc-open-data/99c0f6d5-cbf3-4f4b-8572-e8be07518d79,s3://idc-open-data/66c22a8c-b29a-4a13-bcf1-fb12f6139bac,s3://idc-open-data/ac1c80d4-e11c-4203-8c8a-5009b045d18b,s3://idc-open-data/f57c1ac9-2d19-4861-a3fa-247c385a2f59,s3://idc-open-data/6936a577-eb26-4024-b492-59f15c725652,s3://idc-open-data/f01dcf47-b34d-4e34-b121-1927747c7af3,s3://idc-open-data/835d740c-f130-47a8-a5af-713b3e2257a0,s3://idc-open-data/4bfdb5f1-c00a-4e45-b028-e7b439633c28,s3://idc-open-data/8a31ee63-c33c-4c89-a422-cc1b44c2ef59,s3://idc-open-data/0f8d95a5-66a9-452e-8bc0-5ad357a49213]
In case of IDC, we guarantee there is one and only one series in each bucket folder, so one could optimize loading by, for example, creating one entry on the left for each series, and incrementally populating each item one by one. But in general, of course, there can be any kind of mix of instances across buckets.
I guess this speaks for the advantages of the DICOMweb interface, where you could query metadata for each series, instead of having to fetch all of the study into the browser to make sense out of it.
As I said, I am not sure there is a solution, but I wanted to raise this issue since loading for that case above is rather slow. You should at least be aware of this.