Model does no contain samples when using vb with init function

I'm trying to estimate a large correlation matrix (dimensions about 100x100), which makes Stan fail to find initial values, I think because filling all entries with random values from (-2, 2) doesn't give a valid correlation matrix, even if you try 100 times. My idea for a workaround was to choose the initial values using the R package randcorr. However it seems that vb doesn't like having a custom init function and returns a model without any samples. Here is a minimal example to reproduce the problem:

library(rstan)
library(randcorr)

model_code <- '
data {
 array[100] vector[100] y;
}
parameters {
 cholesky_factor_corr[100] y_corr_chol;
}
model {
 y_corr_chol ~ lkj_corr_cholesky(4);

 vector[100] zero = rep_vector(0, 100);
 y ~ multi_normal_cholesky(zero, y_corr_chol);
}
'

mod <- stan_model(model_code = model_code)

initf <- function() {
	list(
		y_corr_chol = t(chol(randcorr(100)))
	)
}

fit <- vb(
	mod,
	cores=1, chains=1,
	init = initf,
	data = list(
		y = matrix(rnorm(100 * 100), 100, 100)
	)
)

> fit
Stan model 'anon_model' does not contain samples.

> sessionInfo()
R version 4.5.1 (2025-06-13)
Platform: x86_64-pc-linux-gnu
Running under: Arch Linux

Matrix products: default
BLAS:   /usr/lib/libblas.so.3.12.0
LAPACK: /usr/lib/liblapack.so.3.12.0  LAPACK version 3.12.0

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
 [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

time zone: Europe/Vienna
tzcode source: system (glibc)

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

other attached packages:
[1] randcorr_1.0        rstan_2.32.7        StanHeaders_2.32.10

loaded via a namespace (and not attached):
 [1] vctrs_0.6.5         cli_3.6.5           rlang_1.1.6
 [4] processx_3.8.6      RcppParallel_5.1.10 glue_1.8.0
 [7] gridExtra_2.3       ps_1.9.1            pkgbuild_1.4.7
[10] stats4_4.5.1        scales_1.4.0        grid_4.5.1
[13] tibble_3.2.1        lifecycle_1.0.4     QuickJSR_1.7.0
[16] inline_0.3.21       compiler_4.5.1      codetools_0.2-20
[19] RColorBrewer_1.1-3  Rcpp_1.0.14         pkgconfig_2.0.3
[22] farver_2.1.2        R6_2.6.1            pillar_1.10.2
[25] parallel_4.5.1      callr_3.7.6         magrittr_2.0.3
[28] loo_2.8.0           tools_4.5.1         gtable_0.3.6
[31] matrixStats_1.5.0   ggplot2_3.5.2

Start at the RStan vb() entry point and reproduce the supplied minimal example with the custom initf function and 100x100 data. Trace why the returned fit contains no samples; done means the same invocation completes with samples available in fit.