The bug is caused by the "Chain Pull Range Suppression" effect which causes all gap closing abilities to have no range (this goes for ultimates such as DK leap too). In Imperial City you get affected by this effect everytime you transfer between zones. In battlegrounds you´re affected by something similar before the match begins. Note that this bug can´t be fixed by reloading UI or relogging. You can work around the issue however and here is what you need to do:
1. Make sure to remove the skill/gap closer from your bar before you enter Imperial City or a battleground, and have it remain unslotted while you´re in the "safe areas" (where you have the Chain Pull Range Suppression effect on you). Another thing I´ve noticed is that you shouldn´t let the skilline where the gapcloser is, be the last skilline you looked at before entering these areas. So if I want to be able to use Toppling Charge, the aedric spear skilline can´t be the last skilline I opened up before entering the "safe area".
2. Now make sure to leave the "safe area" before re-slotting your gapcloser. In battlegrounds you will only have to do this process once since the "chain pull range suppression" only exists before the game starts but not while it´s in progress.