ERR value is not a valid float

[Airee]

When navigating to a thread occassionally an error will appear saying:

ERR value is not a valid float

Any ideas? I haven't done any major reconfiguration recently.
Furthermore, I got this error in my nodebb log:

node_redis: Deprecated: The ZADD command contains a "null" argument.
This is converted to a "null" string now and will return an error from v.3.0 on.
Please handle this in your code to make sure everything works as you intended it to.

Any ideas? Clearly it's an issue with my Redis database but I need to know how to fix it as it accompanies weird sorting issues which really are throwing people off and using the site annoying to use.