Yes, when I removed the missingstring=" " option then the tryparse worked. With the missingstring on, it errors
julia> tryparse.(Float64,isc[!, :smajax])
ERROR: MethodError: no method matching tryparse(::Type{Float64}, ::Missing)
Closest candidates are:
tryparse(::Type{Float64}, ::String) at parse.jl:247
tryparse(::Type{Float64}, ::SubString{String}) at parse.jl:252
tryparse(::Type{T}, ::AbstractString) where T<:Union{Float32, Float64} at parse.jl:287
Yes, it’s the explanation I gave abote. passmissing(tryparse(Float64, missing)) returns missing instead of nothing.
I think you mean passmissing(tryparse)(Float64, missing) - we’re not having a lot of luck with correctly typing this out today 
FWIW I downloaded your data and am getting all String columns (irrespective of any missing values - it seems to me that missingstrings = [" "^i for i in 1:8] catches them all), so not sure how you’re managing to get any Floats 
There are a few other discussions I found on here around fixed width files which suggest CSV.jl should be able to handle them with ignorerepeated = true, but that doesn’t help in my tests either. Maybe there should be a trim_whitespace kwarg like in readr’s CSV parser.
Sorry had to leave for a Zoom.
I’m Windows. I don’t see why we would have different column types with the same fime and same commands. Ah, I’m also on “v1.6dev”
Edit: nope, tried with 1.5 and still get Floats and Strings
julia> isc = CSV.File("isc-gem-cat.csv", header=93, normalizenames=true, dateformat=Dates.DateFormat("yyyy-mm-dd HH:MM:SS.sss")) |> DataFrame
39160×31 DataFrame
Row │ _date lat lon smajax sminax strike q depth unc q_1 mw unc_1 q_2 s mo fac mo ⋯
│ DateTime Float64 Float64 String String String String Float64 Float64 String Float64 Float64 String String String String St ⋯
───────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
1 │ 1904-04-04T10:02:34.56 41.802 23.108 8.6 6.6 164.2 B 15.0 4.8 C 6.84 0.4 C d 2.30 19 b ⋯
2 │ 1904-04-04T10:26:00.88 41.758 23.249 8.3 6.9 15.2 B 15.0 4.8 C 7.02 0.4 C d 4.20 19 b
3 │ 1904-06-25T14:45:39.14 51.424 161.638 33.6 18.7 116.2 C 15.0 25.0 C 7.5 0.4 C d 2.60 20 b