It doesn't happen always, but sometimes it does. When Survivors leave the Transmitter circle area, its effect/icon is still active. Even when Transmitter itself disappears from the map, its effect/icon is still active on Survivors.
Here's a video of that happening: https://mega.nz/file/kM9TgbQQ#SphGCNGI5Gy8zz3KS26MuJfJLnXIbsUVhTbbNR1TwsE
Not the best demonstration due to the video quality (can't see the border of the area of effect properly), but at least you can clearly see that after it expires from the map in the beginning of the next wave, its icon is still active on Survivors.
I have also submitted a bugreport via the in-game feedback form.