When running with Smooth Font, the attack sometimes causes all characters to turn black in the Chinese case

You say it happens sometimes, can you provide a way to replicate the bug? Some screenshots of when it occurs and when it doesn't may be helpful as well.

We usually cannot be aware of it in a timely manner, like 'it didn't happen before we discovered it', but I am willing to provide a screenshot of the error occurring before it happened (later on Discord)

Furthermore, it is necessary to provide additional feedback that this mod may also cause reinforcement failure of some tinkers constructions (such as glowing, bheading cleavers, which require multiple materials). It cannot be ruled out that it is the result of multiple mods working together. However, in my case, this issue occurred after installing DDD

The problem would likely just be the interaction of Smooth Font with DDD, as I have done a lot of testing with DDD and tinkers and found no issues

My modpack has the same problems either.
When DDD is working with SmoothFont mod in Minecraft 1.12.2, All the tooltips on the items will turn black if a player hit some entities or open a gui for 1-2 times.
When quit the gui in the game, it MAY return to normal. But it will happen again.