In order to bond multiple internet connections together there must be a Peplink on each side and a SpeedFusion VPN established between them. Here is a knowledge base article to describe this in more detail:
should i understand that this is a normal behavior? based on the document that you sent??
When there is only a single data transfer (e.g. when downloading a file by a single user), traffic will take place over one WAN link. In this case, the speed of the corresponding WAN link limits the data transfer rate.
You should indeed get the bonding in this scenario. Please open up a support ticket with us here so we can look at both sides to investigate the issue.