Quite long time ago, something bad happened with these dance emotes in which a position is changing during the cycle (for example Mercy’s and Tracer’s one). With every cycle they are moving further and further away from the place they started. Also, they are now unusable on moving objects (like boats in Rialto), because characters are almost instantly pushed to the edge of them and then the emote is stopping, thus making impossible to do ‘party boats’ 
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Also, something even worse happened to Lucio’s emote. If started at certain angle (just before he turn his legs straight), his legs are bending in all possible directions 
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