B2 and Cloudflare, some users say CF link doesn't work

Hello there,

I am serving some files on my website via B2 + Cloudflare.
Some users got in touch with me saying that the downloads stop working after around 30mbs.
Then I asked them to access the backblaze b2 link directly and it worked without any problems.

What are the things I can check here to find out what is happening?

Thank you