Warning messages (from lme4?) for posterior_epred() with newdata

Dear Stan-Community,
I’m using rstanarm for Multilevel Regression and Poststratification (MRP) with functions stan_glmer() and posterior_epred(). The code does run without error and produces results that make sense. However, when running posterior_epred() with the argument ‘newdata’ specified, R silently stores a list object called ‘curWarnings’ in the environment. It contains 2 string elements: “failure to converge in 1 evaluations” and “convergence code 4 from Nelder_Mead: failure to converge in 1 evaluations”.
After a Google search it seems that it originates in some lme4 function.
I was wondering if these warnings are actually relevant for my analysis and if so, what exactly they mean?
Thank you!

Here is a reprex:


# Create dataset
dat <- data.frame(y = sample(c(0,1), 100, replace = T),
                 x = sample(c(1,2,3), 100, replace = T))

# Fit model
fit <- stan_glmer(y ~ (1 | x),
                  family = binomial(link = "logit"),
                  data = dat,
                  seed = 505)

# posterior_epred without newdata
pred <- posterior_epred(fit, draws = 100)

# Create newdata
new <- data.frame(x = c(0,1))

# posterior_epred with newdata
pred_new <- posterior_epred(fit, newdata = new, draws = 100)

# Print returned object with warnings

Operating System: Windows 10
R Version 4.1.1
rstanarm Version: 2.21.4