[R] [effects] Wrong xlevels in effects plot for mixed effects model when multiline = TRUE

[Gerrit Eichner]

Dear list members,

I observe a strange/wrong graphical output when I set the xlevels
in (e. g.) allEffects for an lmer model and plot the effects with
multiline = TRUE. I have compiled a reprex for which you need the
lmer model and the environment in which the model was fitted. They
are contained in the zip file at
https://jlubox.uni-giessen.de/dl/fiSzTCc3bW8z2npZvPpqG1xr/m-and-G1.zip
After unpacking the following should work:

m <- readRDS("m.rds")   # The lmer-model.
G1 <- readRDS("G1.rds") # Environment in which the model
                          # was fitted; needed by alaEffects.
summary(m) # Just to see the model.

library(effects)
aE <- allEffects(m, xlevels = list(gProt = 1:6 * 30))
                      # Non-default values for xlevels.

plot(aE)                      # Fine.
plot(aE, x.var = "Age")       # Fine.
plot(aE, lines = list(multiline = TRUE))  # Fine.

plot(aE, lines = list(multiline = TRUE),
       x.var = "Age")        # Nonsense.


Anybody any idea about the reason, my mistake, or a
workaround? Thx for any hint!

   Regards  --  Gerrit


PS:
  > sessionInfo()
R version 4.0.2 (2020-06-22)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 18363)

Matrix products: default

locale:
[1] LC_COLLATE=German_Germany.1252  LC_CTYPE=German_Germany.1252
[3] LC_MONETARY=German_Germany.1252 LC_NUMERIC=C
[5] LC_TIME=German_Germany.1252

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

other attached packages:
[1] effects_4.2-0 carData_3.0-4

loaded via a namespace (and not attached):
   [1] Rcpp_1.0.5       lattice_0.20-41  MASS_7.3-53      grid_4.0.2 
DBI_1.1.0
   [6] nlme_3.1-149     survey_4.0       estimability_1.3 minqa_1.2.4 
nloptr_1.2.2.2
[11] Matrix_1.2-18    boot_1.3-25      splines_4.0.2    statmod_1.4.34 
lme4_1.1-23
[16] tools_4.0.2      survival_3.2-3   yaml_2.2.1       compiler_4.0.2 
colorspace_1.4-1
[21] mitools_2.4      insight_0.9.5    nnet_7.3-14

---------------------------------------------------------------------
Dr. Gerrit Eichner                   Mathematical Institute, Room 212
gerrit.eichner using math.uni-giessen.de   Justus-Liebig-University Giessen
Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
http://www.uni-giessen.de/eichner