Can't load 'rstanarm' package on Windows 10 (using Anaconda Prompt)

Summary:

A short summary (no more than a sentence or two).

When trying 'library(rstanarm)', the library fails to load and am told "object 'm' not found

Description:

A full description of the problem (or question).

install.packages("rstanarm")
trying URL 'https://mirror.aarnet.edu.au/pub/CRAN/bin/windows/contrib/3.6/rstanarm_2.21.1.zip'
Content type 'application/zip' length 11181503 bytes (10.7 MB)
downloaded 10.7 MB

package 'rstanarm' successfully unpacked and MD5 sums checked

The downloaded binary packages are in
C:\Users\zelez\AppData\Local\Temp\RtmpErHdtB\downloaded_packages

library(rstanarm)
Loading required package: Rcpp
Error: package or namespace load failed for 'rstanarm' in .doLoadActions(where, attach):
error in load action .A.1 for package rstanarm: is(module, "character"): object 'm' not found
In addition: Warning message:
package 'rstanarm' was built under R version 3.6.3
library(rstanarm)
Error: package or namespace load failed for 'rstanarm' in .doLoadActions(where, attach):
error in load action .A.1 for package rstanarm: is(module, "character"): object 'm' not found
In addition: Warning message:
package 'rstanarm' was built under R version 3.6.3

Reproducible Steps:

If applicable, the steps required to reproduce the issue. If you have a reproducible example, please include it.

install.packages("rstanarm")
library(rstanarm)

RStanARM Version:

The version of the rstanarm package you are running (e.g., from packageVersion("rstanarm"))

2.21.1

R Version:

The version of R you are running (e.g., from getRversion())

3.6.1

Operating System:

Your operating system (e.g., OS X 10.11.3)

Windows 10 Pro 18363.959

No source file or test is named. Start by running install.packages("rstanarm") and library(rstanarm) with R 3.6.1, rstanarm 2.21.1, and Windows 10, then investigate the reported namespace load error and version mismatch. Done means the package loads successfully on the reported setup.