BALANCE210 Not performing normally for fusing 2 WAN sources and 40,000 concurrent sessions

Hi there PEPLINK Gurus/Users,
I recently bought PEPLINK BALANCE210 to bond 2 of my internet sources ( burst FTTH from 2 competing TELCOS). WAN1 is 100Mbps and WAN2 is 100Mbps. I noticed that when I do speed test, it doesn’t show a 200Mbps download speed, though, each WAN max burst speed is 200Mbps.
Also, since there are around 100 users, concurrent sessions reaches 40,000 to 50,000, thus, making the CPU load pegged at 99 to 100%. This, causes the warning of DNS FAILED, frequently. When I reboot the system, this warning is gone.
I’m no longer using this device for my 100 users, but use the TP-LINK Load Balancer TL-ER5120 instead, and it didnt HANG or causes the CPU load to reach 100%.
Can anyone have experience with BALANCE380 to aggregate 2 WAN sources which are local physically?
thank you.