I have manacles at 200 but they seem to not be functioning. when I take alot of damage no golden bracers appear.
Um probably the mystical symbol is negating some of that damage preventing the manacles bracers from activating . I'm no tank tho but I've heard of such things with these two arts. I am sleepy lol so hopefully a tank can chime in and help you bud.
Manacles, Mystical Symbol and Everyman are the FOTM bread and butter artifacts for tanking right now. They all work well together. Unless there's a bug, you shouldn't be having problems.