Tested on MT6000 and MT3000 as well:
Both problems:
1 - Full Cone NAT not working when using PPPoE
2 - 2.4GHz speed on (not so) old devices is garbage. Take a look:
Device: Huawei P30 Pro (Android)
closed source firmware speed test on 2.4GHz:
Great speed, low latency!
open source firmware speed test on 2.4GHz:
I just wanna cry! It's a mess!