I've come across what looks like a conflict between Scaling Health and the InGame Info XML mod. When the InGame Info XML HUD is enabled the Scaling Health difficulty meter vanishes. Disabling the InGame Info XML HUD causes the difficulty meter to reappear. I have B:"Render Difficulty Meter Always"=true. All InGame Info XML settings are default.

It can be reproduced with the the following minimal setup (as of this post, the most recent versions of everything for Minecraft 1.10.2):
Minecraft 1.10.2 + Forge 12.18.3.2297
ScalingHealth-1.11.x-1.0.6-48.jar + SilentLib-1.10.2-2.1.3-58.jar
InGameInfoXML-1.10.2-2.8.1.89-universal.jar + LunatriusCore-1.10.2-1.1.2.38-universal.jar

Hopefully it's not too complex a fix. Let me know if you need any other information.

this is happening to me also but it only shows up in the F3 Screen but for 1.10.2
all recent versions as well
ScalingHealth-1.11.2-1.0.8-52 + SilentLib-1.10.2-2.1.5-63
InGameInfoXML-1.10.2-2.8.1.89-universal + LunatriusCore-1.10.2-1.1.2.38-universal

I don't think there's anything I can do to fix this. InGameInfoXML is canceling several overlay rendering events before they get to Scaling Health.