Are there any other issues related to H/W Performance?
Generally, in mid-sourcing deployment model case, there can be some error like this.
And it is already commented on the AC document.
or are there any issues related mx rules configuration?
If you can share more detail info (error logs or something which can help understanding this issue. Of course it doesn't have to be explained client's identity), maybe we can check this issue based on other project experience.