Reproducer

foo = DBM:NewMod("Foo")
t = foo:NewCDTimer(123, "test")
t:Start("v10-20")

With enlarge threshold set to 10 seconds makes it starts out as large (good), but once it reaches 10 seconds remaining it seemingly tries to enlarge again and looks like a 5-10 variable timer.

Actually not specific to the threshold, it seems to be always incorrect once the "restart" as a 10 second large timer happens?

Seems fixed by d8b1bc3

Actually, this is exactly what I mentioned on Discord. On Classic anim, this repro case works flawlessly:

NoAnim however, misbehaves and since I encountered enlarge bugs with the DBT codebase prior to variance implementation, I left it alone and assigned it as unrelated (example shown below with bars resetting width, or fake enlarging when no large bars enabled, which also happened with variance code, and looked exactly like your bug, just with the enlarge large anchors enabled):

I still think this is is a deeper bug than just the variance check inserted, but I'd have to take a deeper look into DBT... I haven't looked it at in a while

Bug already described here: DeadlyBossMods/DBM-Unified#135