Mosaic fails when reading rasters from disc but not from memory - r

Question

I ran into a weird issue when trying to make a mosaic from several hundred rasters. The satellite imagery I'm using is not perfectly aligned or shares the exact same resolution, so I followed the steps found here to resample my rasters and then mosaic them.
I started off testing on a subset of only four images and had no problem doing this (had to manually calculate the full extent since unionExtent and the newer union only allows two extent arguments):
# Reading raster files
rst <- lapply(list.files(), FUN = stack)
# Extracting individual extents
rst_ext <- lapply(rst, FUN = extent)
# Calculating full extent
xmin_rst <- c(); xmax_rst <- c(); ymin_rst <- c(); ymax_rst <- c();
for (i in 1:length(rst_ext)) {
xmin_rst <- c(xmin_rst, rst_ext[[i]]#xmin)
ymin_rst <- c(ymin_rst, rst_ext[[i]]#ymin)
xmax_rst <- c(xmax_rst, rst_ext[[i]]#xmax)
ymax_rst <- c(ymax_rst, rst_ext[[i]]#ymax)
}
full_extent <- extent(min(xmin_rst), max(xmax_rst),
min(ymin_rst), max(ymax_rst))
# Creating raster from full extent and first rasters' CRS and resolution
bounding_rst <- raster(full_extent,
crs = crs(rst[[1]]),
res = res(rst[[1]]))
# Resampling rasters to match attributes of the bounding raster
rst_resampled <- lapply(X = rst, fun = function(x) {
target_rst <- crop(bounding_rst, x)
resample(x, target_rst, method="bilinear")
})
# Creating mosaic
rst_mosaic <- do.call("mosaic", c(rst_resampled, fun = mean))
That worked out OK, but of course, I didn't want to save all those rasters in my memory since I'd run out of it. I decided to save them in a new folder and re-read them as a stack, then make the mosaic.
# Function to crop, resample and write to a new GeoTIFF
resample_write <- function(x) {
target_rst <- crop(bounding_rst, x)
x <- resample(x, target_rst, method="bilinear")
save_name <- gsub("\\.1",
"_resampled.tif",
names(x)[1]) # Modifying name of 1st band
writeRaster(x,
filename = paste("../testing_resampling/",
save_name, sep = ""),
format = "GTiff")
}
# Running the function
lapply(rst, FUN = resample_write)
# Reading resampled images
setwd("../testing_resampling/")
rst_resampled2 <- lapply(list.files(), FUN = stack)
## Making the mosaic
rst_mosaic2 <- do.call("mosaic", c(rst_resampled2, fun = mean))
This gives the following error:
> rst_mosaic2 <- do.call("mosaic", c(rst_resampled2, fun = mean))
Error in compareRaster(x, extent = FALSE, rowcol = FALSE, orig = TRUE, :
different origin
I was able to get around it by setting the increasing the tolerance argument of mosaic to 0.4 but still don't understand why rst_resampled1 and rst_resampled2 yield different mosaic results.
Comparing them both with compareRaster and cellStats tells me that they're exactly the same.