I'm sitting at 369 light and I've decrypted god knows how many legendary engrams and sadly, they have all been resolving at 365!
I don't know if this is a known issue or what, but I've personally been encountering on every engram. it's pointless for me to decrypt. I'll provide a video link after my next stop to the blue bastard.
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That's the highest legendary engrams decrypt into. That isn't an error or a bug. You can find the patch notes from last week in the following link: https://www.bungie.net/en/News/Article/45265/7_Destiny-Rise-of-Iron