LTE5398-M904 Connection & WiFi problems

Hi,
I have a strange problem with my LTE5398-M904.
For example when I have several devices connected on WiFi (2 smartphone, 1 tablet and 1 imac) if I download something from any device the others will be disconnected from WiFi and after a few minutes LTE connection is not avaiable anymore (but all lights on the router are green) and I have to reboot the router to have LTE connection working again. I have this issue on both WiFi 2,4ghz and 5ghz.

I am on firmware V1.00(ABQV.2)C0 and LTE Module EG18EAPAR01A08M4G

I have tried my sim card on other LTE routers (huawei, tplink and mikrotik) and everything is working well. I also tried to reset to default settings but I have always the same problem. 

Can anyone help me please?

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