Memory consumption of Docker Wireguard during and after backup

Hello, I use Wireguard, among other uses, to make offsite backups. Of course that requires sending GBytes through the VPN. I have noticed a huge increase of the memory consumption of the container during the backup (2.4 GB instead of 40 MB). That is no problem to me. But that memory consumption remains high after the backup has ended. Is this an expected behaviour ?
So I have decided to restart the container at the end of each backup.