HEVC's Long-term reference picture can’t be used in 7th Gen nvenc(A4000, GTX2070,…)?

In our application, the first frame will be set as the long-term reference frame, and all other frames will only refer to the long-term reference frame. When I use the 6th Gen nvenc(Tesla V100, GTX1070,P2000…), I use ltrTrustMode=1, it can work well.

But it can’t work on the 7th Gen nvenc. Maybe this mode is deprecated now. So, I use ltrTrustMode=0, and mask the first frame(or other frame) as LTR frame, it still can’t work.

And then, I run the same application on the 6th Gen nvenc, it can work.

So, I want to know, does the 7th Gen nvenc not support LTR frame now?