When my character is moving and i start a sequence, i do the following thing :
Play node on my sequence, then , Set InputModeUIOnly ( no widget and Lock Always on Mouse )
And when sequence end : SetInputModeGameOnly
Thing is, if the player press forward before sequence start, and release the key durring the cinematic, when cinematic end, player go forward without stopping even if the forward key has been released, i have to press forward again and release it to have the player to stop.
Using CinematicMode fix the problem, but if i want to simply spawn a pop up the player has to interact with, the problem is the same. Is there a way to release all input or something ? ( i can take care of disabling the effect of the release in my code ) but this gost key effect is really a problem 
it looks like this issue
i use binaries from luncher, c++ project, 4.19.2