Hello there
i hope you have a good work day
I have an issue in making load balance with one ADSL line and other LTE , both of lines are Double NAT from ISP (ISP provides me with ip start wit 10.101.....)
so when i apply NTH or PCC methods on RB951 , i can only get a maximum of 8M of both lines (Normally should get 20M), I.e.: not get of all speed , but when i plug only one line i get a full speed.
I hope that find a solution

That sounds like a weak router that cannot deal with the traffic volume without using fasttracking in the firewall, or like a powerful enough router where you forgot to disable fasttracking so only few packets actually take the proper way. The fact that we talk about RB951 here suggests that it is the former case, the fact that disconnection of one of the WANs, without touching the configuration I guess, supports the latter explanation.

So if there is a chain=forward action=fasttrack-connection ... rule in your firewall, disable it and see what the outcome will be. But doing so may just transform variant 2 (speed lowered due to sending packets the wrong way due to fasttracking) into variant 1 (router being too weak to deal with the bandwidth without fasttracking). So you may need a combination of both approaches, or a new router.