I have a TP-Link TD-W8980 v1 router, two Huawei P8 Lite devices and another bunch of devices working pretty well.
I was testing on https://fast.com, both p8 remain like 10 seconds on the page with 0 Kbps speed, and then reach awful speed (below 1 MB).
Turning bluetooth off fixed the issue, but after renabling it is still working.