Sometimes the revive syringe is not working, won't revive players at a close enough distance which has worked lots of other times. Question: Does the drawing fluid from the vial animation have an effect? or is it only an animation?
Drawing fluid from the syringe has no effect on reviving. If anything, it does more harm than good, as it slows revives down (and on top of that you lose momentum in the process). However, it's not fully without a use. The longer you hold the syringe, the more damage you will deal to enemies once you try to stab them with it. Fully "loaded" syringe can kill a Sentry with one hit.
On what causes the syringe to not work: it usually is caused by a) not aiming at torso area or b) body going through parts of environment. The second case includes things like bushes or small boxes.
