How to find the first time step (column 1) when the values between time steps in column 2 is of a certain difference

General Usage
9

Unfortunately, when I adapt the code to my actual data I get

TypeError: non-boolean (Missing) used in boolean context
in eval at base\boot.jl:373 
in top-level scope at untitled:35
in findfirst at base\array.jl:2002
in findnext at base\array.jl:1951

The code is

df_high_1.difference = lead(df_high_1.bioS1) .- df_high_1.bioS1 # this works
food_web_1_8_8 = findfirst(≈(1e-10), diff(df_high_1.difference)) # this causes the error

Any idea what could be happening?

Could this mean the condition is never met?