Strange result from optimisation?

[LHMarshall]

While generating some test data I have seen some strange model fitting results from mrds. Something to come back to when we look to improve the optimiser perhaps? Recording here so we have code to reproduce. It's strange because the data are generated from a half normal and it is not a particularly complex model. There is no association between distance and size.

set.seed(112)
# generate some data to test on
dat <- data.frame(Sample.Label = 1:10)
dat$Region.Label <- c(rep(1, 5), rep(2, 5))
set.seed(123)
dat2 <- dat[sample(1:nrow(dat), nrow(dat), replace=TRUE), ]
dat2$object <- 1:nrow(dat2)
dat <- dat[!(dat$Sample.Label %in% dat2$Sample.Label),]
dat$object <- NA
dat <- rbind(dat, dat2)
dat$save.ind <- 1:nrow(dat)

#set.seed(127) or set.seed(112) here to see stange results
dat2 <- dat
dat2$Region.Label <- paste("YEAR", as.character(dat2$Region.Label), sep = "")
dat2 <- rbind(dat2, dat2, dat2)
dat2$distance <- abs(rnorm(nrow(dat2), 0, 25))
dat2$Effort <- 1000
dat2$Area <- 100
dat2$size <- rpois(nrow(dat2), 20)
dat2$object <- 1:nrow(dat2)

conversion.factor <- convert_units("meter", "meter", "square kilometer")

fit.ds <- ds(data=dat2,
             truncation=50,
             key="hn",
             adjustment=NULL,
             convert_units=conversion.factor,
             formula=~size)

plot(fit.ds)
fit.ds$ddf$par

[erex]

Ran this verbatim code using

> sessionInfo()
R version 4.3.2 (2023-10-31 ucrt)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 11 x64 (build 22631)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.utf8  LC_CTYPE=English_United States.utf8   
[3] LC_MONETARY=English_United States.utf8 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.utf8    

time zone: Europe/London
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] Distance_1.0.9 mrds_2.3.0   

and produced this result

> fit.ds$ddf$par
X.Intercept.         size 
  3.67491262  -0.02612638