Some files are missed if send many requests together

[vokson]

Good Day,
I try to download many small files (<50 Kb). My JS sends 20 requests togther in order to download 20 files. I have checked that all 20 responses have been received correctly. I have also checked that for 20 files tempLinks in file-download.js have been clicked and then removed after timeout.
Problem is I can't download all requested files. More over each time I download different count of files 13/20, 16/20, 19/20. Rarely 20/20. I tried to increase timeout in file-download.js, but it didn't helped.
If I decrease count of simultaneous requests, situation becomes better. If count of simultaneous request = 1, I always receive 20 files correctly.
Please, help. Do you have any idea?

[vokson]

I found, that problem in Chrominium engine (Chrome, Edge). Firefox works fine. Safari - don't know.