VPN download speed degradation

[doom]

Good day!
We have R82 JHF107 VPN gate. E89.10 client. Discovered one problem:
Client with 400 Mbit/s internet link connected through VPN have only 1-3 Mbit/s speed downloading the file using Microsoft-DS TCP 445 port.
If he downloads the same files through VPN but another file sharing space via HTTPS TCP 443 it is ok and speed if full.
Client is located a little bit far away from VPN server, around 5000 km, ping via VPN around 200-300 ms.
Without VPN this user have full speed downloading files from Internet.

I have see no errors in the log during his connection.
I download the same files by myself via TCP 445 (the same rule in the FW policy) and do not get speed degradation.
I have the same corporate notebook and OS Windows config/Updates as this user.

Any ideas what could cause this speed droping?
I think about User's Internet provider but which facts could I show proving this? And how it is possible to affect only TCP 445 port in VPN and not others?

[Timothy_Hall]

Either the person experiencing the degradation has a sub-1500 MTU somewhere on their network path, or they are using an older version of the SMB protocol that doesn't perform well across the Internet.  These same issues can occur when using Check Point SASE, which is covered in my upcoming book: