AWR2944EVM: AWR2944EVM use TRIG_GPIO to trig frame, why it just can trigger only one frame

hello experts:

    when i use awr2944 evm board base a high conner project, i want to use SYNC_IN pin to trig one frame manually. 

first, i set the SYNC_IN pin enable

second, i set the frame config with sync_in trigger

when i push the SW2 button at first time , one frame can be triggered, and the data path works,

but, when i push the SW2 again, there is no frame be sent.

i check the DPM_frameStartISR,  it just be involked one time;

the same confg can work in the AWR1843 board:  one up edge on the sync_in, one frame be sent.

is there any key step i missed ?  please give me some suggestion.

thanks.