AC68 not compatiable with 4G dongles in Finland.

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Currently, I have AC68 and HUAWEI E3372 4G dongle. The problem is all Google based service are extremely slow, like Gmail, Youtube, Google Maps, Keep, Photo... But when I directly connect the 4G dongle to the computer, everything is fine. Then I tried to connect AC68 to my mobile phone's hotspot, everything is fine too. Only when they work at the same time, the problem appears. I updated the firmware of AC68 to the latest and also some old versions, and Merlin, no help. I changed AC68 to AC87, no help. I tried on TP-LINK VR900, no help. I replaced HUAWEI E3372 with ZTE MF831, no help. Please help.