Hello,
Apparently, your source which apparently is a live stream in nature is behaving like a VOD (as can be seen when your source is directly played in a media player, there is a "seek" capability in it.)
EMS current cannot handle this kind of instances as it is the first time we’ve handled this kind of input.
We’re filing a ticket for this one, so that we can make fixes in the future. Thank you for your continued patronage.