WebDAV doesn't work

Seafile Server Pro 6.3.13 (3 user) (not sure how to actually install 7.x in synology with several containers and synology’s strange DSM).
Running in Docker on Synology DS218+. RAID1 SHR on HDD(no SSD)
WebDAV enabled. Connection is directly to instance’s webdav port - ip:8080 (also tried external nginx as reverse proxy, nothing changes)
Seafile windows client appears to work and rather good.
WebDAV appears to work.
I imported (via seaf-import) Joplin’s data to library and Joplin doesn’t sync via WebDAV. attempt to open joplin’s directory via browser takes a lot of time (>10 minutes). python eats about 2 Gb of RAM.
Joplin’s data directory contains approx 200k very small files in one directory (total size approx 10 Gb).
How to make Seafile webdav work in this situation?

Installing 7.1 from scrath doesn’t fix issue. .

It may be due to the fact that you’re opening a folder with a lot of items in it. Seafile needs to load the entire directory list into memory.

7.1 Pro + all data moved to USB3 SSD for testing.
Seafile’s UI works much faster than before (approx 10 seconds).
Seafdav responds in approx 20 seconds.
Response takes only 55 Mb uncompressed.
Still very slow. memory abuse could be acceptable but why such slow response time?

Maybe the most time is spent on parsing the JSON data in the folder object.