Also related to this: https://forums.unrealengine.com/t/is-there-a-draw-limit-to-drawdebugstring/480412
This took me a few hours to figure out but finally I discovered there is a default “draw debug string” limit - 128, you can change it through the console (use “`” to access, if hidden) and use the following command:
r.DebugSafeZone.MaxDebugTextStringsPerActor [number of max draws here]