Would it be possible to add a config to toggle this system message off? I changed some attributes for infernal mobs in our world, and I can't find a way to get the console spam to stop. It doesn't seem to affect the server either, so simply turning it off would be allright.

The code change in 4444501 seems to have made it so the console spam now ends up being "Was [], now trying to set [{modifiers}]"
Seems like the check at https://github.com/AtomicStryker/atomicstrykers-minecraft-mods/blob/master/InfernalMobs/src/main/java/atomicstryker/infernalmobs/common/MobModifier.java#L136 should check for an empty string as well, and skip logging in that case.

Awesome, thanks!

Aye. But i already fixed this c08c265

And since i could already anticipate the next request the same hotfix was pushed to the 1710 version branch

As a solution for myself, I edited out that elseif, and remade jar. But I would like to see the option to turn it off, as a debug config perhaps.

Does never happen (or should not) unless you load an existing save with a differing modifier set. If you insist on doing something like this, i would suggest killing all entities on the server. Although i do see the issue - Infernal Mobs will keep logging this and not "fix" the error.