I think I've figured out what's going on here and fixed it for the next build.
Setting an animation every tick like in 
Joannesalfa's example is quite common. Usually if you set an animation that is already playing, Construct 2 ignores the action, so the animation plays as expected. r105 fixed a problem where 'Set animation' in an 'On animation finished' event didn't work, but this accidentally changed what happens when you set an already playing animation: now it acts like "rewind to beginning" every tick, which makes the animation get stuck on the first frame. We can't leave it like this because it will break too many existing projects, so I've figured out a way to fix this so both things work. That will go in to r106, but in the mean time you'll have to use a workaround I'm afraid - just add 'trigger once' to your events that set animations, so they don't set the animation every tick. After the next build it shouldn't be necessary any more to do that. Sorry for the trouble!