Low downloading speed of big files from S3 as external storage

Nextcloud version:
Operating system and version: Ubuntu 20.04 LTS
Apache or nginx version: Apache/2.4.52
PHP version: 8.1.2-1ubuntu2.11
This is the environment where my Nextloud is running. I have S3 as external storage.
lately, users have started to complain about low-speed download of big files. I also tested and I have the same problem.
I have a good provider and everything is OK.
Help me to figure out where could be a bottleneck with the downloading speed?

What is the speed up/downstream of your server? What is the speed you get for these downloads?
How big are big files, how fast can you download small files?

In the user’s folder, files or part of files can be cached. If that storage is very limited (compare the remaining storage with the bigness of the files where you start get problems), this might explain why it gets slower.