Orbi cutting speed in half

I'm currently on the 1GB fibe plan with Bell (Canada). Bell is one of those ISPs that force their modem/router abomination on you when you sign up with them (Its called the HomeHub 3000). When I connect my laptop directly (via ethernet cable) to the HH3000 and I test my internet speed via Ookla, I get around 970 Mbps, however when I connect orbi RBR 50 (WAN) to the HH3000 (LAN) and run the orbi in-app speed test I'm stuck around 500 Mbps download. I have tried the following, with no effect:

1- switching the Orbi to AP mode

2- granting orbi DMZ access to RBR through HH3000 and using PPPoE credentials to log in (IPv6 and IPv4) on orbi

3- turning UPnP, SIP ALG, IGMP proxying on and off

4- trying different cables (I tried CAT 5E, CAT 6 and CAT 7)

5- Factory reseting both the HH3000 and teh ORBI and seting up from scratch

to make things weirder, when i connected my laptop (via ethernet)to the ORBI,while the Orbi is connected to HH3000, it hit 945 Mbps download. So I thought it might have been just a bug with the in-app test, but when I connected my laptop to orbi via wifi, it only hit 450 mbps download.

How can I resolve this ?