I’m leveling a falconer. Everything works fine, but after a few mobs I cannot directly cast umbral blades anymore. It’s still getting cast through shadows, but the direct cast is disabled until I re-slot it on the bar. Happens with mouse button as well as key.
The combo I use is dummy, smoke cloud, shift, umbral blades and falconry
I am having the same issue. Worked normally yesterday, but today after newest update this occurs mostly when a skill levels or I level.
I noticed it yesterday before I logged off. Today I checked if the update fixed it, but it reoccured., so I made the post. Have played ~4 hours since then, and it’s fine now 
I am having this issue as well. I havent been able to figure out what causes it but it seems randomly happening in the middle of combat so far. It happened to me probably a dozen times yesterday and half a dozen in 2 hours this morning.
I had the same issue. I am able to re use it if I add it to another slot and press another key. For example if I slot UB on R and it stops working, I can put it on right click and it starts working again. Such a weird bug, I haven’t seen this with any Void knight skill.
I’m having the same issue, but on controller. I’m using the Xbox wireless gamepad and after a while, the binding for Umbral Blades stops working. I am currently using the same combo of skills as the first post. What fixes it, sometimes, is to rebind another skill into umbral, cast it on the new button, cast it on the original button, and then rebind the previous skill back. It started happening after todays update as well.
Same issue here.
I’m getting this quite often, I dont know if its because I have custom keybinds, or using WASD - but my right click skill will stop working untill I changed it out for something else - most recently by ‘loot filter bypass’ key that I’d set as alt stopped working, but changing it did nothing, had to restart to fix.
Also same issue, on PC via Steam, using WASD controls. This has happened several times. I have Umbral Blades set to Right Click, and it will randomly just stop working. A quick fix is to swap out Umbral Blades for another skill or nothing (Blank), then swap it back in. Before I figured that out, I was teleporting back to town, then back to wherever I was fighting, and that seemed to work too, but was much more annoying to have to do.
Ditto, same issue with Umbral Blades, same solution as others have noted (I just switch the key to another skill and back). I’m on mouse control with Umbral on W - no controllers connected and standard keybinds, if that helps.
Same issue, workaround can be changing the skill to another one and back, can be tricky in some situation 
(Config with left click move and right click Umbral)
I am also experiencing this issue
I also have experienced this and I noticed it happens when I get stunned as I’m trying to use it.
I’m getting this too.
Same issue, no custom anything no gamepad just on a laptop.
Happens every 2-5mins for me and absolutely killed my want to play the game.
Typical rotation is dash forward then cast 2 umbral, smoke bomb, sync strike and dash again somewhere between that almost every mono i gotta run to safety rebind and carry on.
Same issue. What I’ve noticed is that the problem is connected to casting Shift, Smoke Bomb and Umbral Blades at the same time. If you avoid casting all 3 at the same time, the problem doesn’t happen. Update: The problem happened with just casting shift and umbral blades. It might be something related to the shadows
Also, unequipping and equipping your weapon solves the issue as well. So that’s another workaround that might be faster than changing skills.
The issue happens with both the controller and keyboard + mouse. Keybinds have no correlation that I’ve noticed, as the issue persists even when using the default settings.
As my first time playing Last Epoch, I was really confused and it took me a while to understand what was happening. I hope this gets fixed soon.
Gonna try this weapon switch fix, I’m on controller and it’s definitely happening when casting multiple skills