Help needed - Having issues with multiple users PC based VPN Clients when connecting back to their respective corporate networks via the Routers Internet Access. Bandwidth is being compromised rendering the unit virtually useless. When the users disconnect their VPN Clients the bandwidth access is restored. Not sure if this is an issue with our APN, telstra.internet, or if it is a constraint of the MP70 settings. Reaching out to see if there is other experiences of mulitple client VPN’s causing performance issues? I am a Project Manager with enough technical nous to get into and most times out of trouble and would greatly appreciate any insight that can be provided. 
Well after much digging and networking (human) have had feedback the Telstra 4GX LTE Network that the MTU Setting at Auto on the Unit although MTU Auto Setting at 1358 that the MTU Sync rate for want of better terminology with the VPN/IPSec is at 1300 can be potentially impacted by Fragmentation. Have applied a manual MTU Setting on the MP70 at 1300 and the latency/fragmentation seems to have been nullified and full performance gain has been acquired on the Unit and the sub contractors Personal VPNing back to their respective organisations are a 
crew and so am I 8) .
NB: Also amended the APN from Telstra.Internet to Telstra.Extranet with Service Provider updating the SIM Codes - the former NATS and the latter has a WAN IP address assigned -awaiting confirmation if this is a major contributor to the stabilization onsite.