If more than one person is affected, I'd say the problem lies at the HQ. If they are serving a large number of VPN connections they machine doing the work may not have enough CPU power the handle all the encryption work. There are encryption accelerator cards to off load the computation (but they have to be supported by the VPN software).

Pioneer PDP-5020FD, Marantz SR6011
Axiom M5HP, VP160HP, QS8
Sony PS4, surround backs
-Chris