determining the less trustworthy log2fc values

Hello, thanks very much for your package. I just want to follow up on this point from the vignette:
> The large `lfc` values come from groups were nearly all counts are 0

It seems that depending on what my design is, the threshold to separate the "three groups" of log2fc values can be as small as 5. I also got the warnings "“encountered non-positive size factor estimates” and “singular gradient” when I was running glm_gp for the fit, I don't know if it's related. I'm assuming these are still "large lfc values" though they are < 20. Is there a better way you could recommend to separate out the genes with less trustworthy log2fc values than by looking visually?