You are likely experiencing Bufferbloat. Some routers support the fq_codel or CAKE algorithms (CAKE is the latest and greatest). Peplink has fq_codel working under the Mitigate Bufferbloat setting for uploads. It doesn’t currently work for downloads, but my information is that is expected to be fixed in version 9.
I and others wish that this was a higher priority for Peplink, but will be very happy if it is finally fixed in version 9 which hopefully will be out later this year. See my long 2018 thread. The 2nd to last response is from Peplink where they say: “Balance 20/30 doesn’t have this feature at the moment due to some limitations. We have filed this and hopefully it is available in the future firmware release.”
reply more_vert Need Active Queue Management for Bufferbloat (fq_codel)
The most recent Bufferbloat user community request was a few days ago from @Andrew_Williams: “+1 for cake. I’ve been using it on my cellular enabled openWRT boxes with great success. If Peplink would get on the ball with this it would be a huge win for everyone.”
Queue management - fq_codel implementation - Mitigate Bufferbloat
While we wait for fq_codel in version 9 for the Peplink routers which will support it, you may want to experiment with enabling the “DSL cable optimization” feature, which my understanding is prioritizes ping, DNS and TCP ACK packets on uplink and can give you a somewhat better Bufferbloat result: Network->QoS Application, DSL cable optimization.