Hi,
I just got a crash report from someone that occured when logging into the server.
It looks like you are modifying the map of animated renderers somewhere other than the main client thread or from the renderAnimated function (which is more unlikely)
Crash report:crash-2018-08-21_19.36.27-client.txt

I just got a similar error: https://pastebin.com/tWL2FksP