IPSEC slow and trouble after pass from pfCE to pf+

[Globo]

Hi,
first, I have to FW in PfSense CE 2.5.1 with no problems, there are just very old machine.
I collapse, ans I by 2 Netgate XG 7100U with PfSense+.
The back up of my PfSense CE (xml) are translate by the netgate team.
I push the result in the new machine.
Once connected, all is ok, just the remote site have trouble.
The connection to our mail exchanger are slow, to send mail via our SMTP are impossible, some connection to remote server are not possible.
We try to change paramaters, to pass by QAT processor for cryptography...
We try to fix the troubles with netgate support with no result.
After 2 week, support said, the problem come from remote site.
But when I come back to my PfSense CE, no problems.
An idea.

Thanks a lot.

Hervé F.