Appending text to an existing file from inside a parallel loop - r

Question

I'm currently processing some data in parallel as part of a larger loop that essentially looks something like this:
for (i in files) {
doFunction
foreach (j = 1:100) %dopar% {
parallelRegFun}
}
The doFunction extracts average data for each year, while the parallelRegFun regresses the data with maximally overlapping windows (not always 1:100, sometimes it can be 1:1000+, which is why I'm doing it in parallel).
Part of the parallelRegFun involves writing data to CSV
write_csv(parallelResults,
path = "./outputFile.csv",
append = TRUE, col_names = FALSE)
The issues is that quite often when writing to the output file, the data is appended to an existing row, or a blank row is written. For example the output might look like this:
+-----+-------+------+---+-------+------+
| Uid | X | Y | | | |
+-----+-------+------+---+-------+------+
| 1 | 0.79 | 2.37 | | | |
+-----+-------+------+---+-------+------+
| 2 | -1.88 | 3.53 | 3 | -0.54 | 3.32 |
+-----+-------+------+---+-------+------+
| | | | | | |
+-----+-------+------+---+-------+------+
| 5 | -0.18 | 1.45 | | | |
+-----+-------+------+---+-------+------+
This requires extensive clean-up afterwards, but when some of the output files are 100+MB it's a lot of data to have to inspect manually and clean. It also appears that if a blank row is written, the output for that row is completely missing from the output - i.e. it's not in the data that gets appended to an existing row.
Is there anyway to get the doParallel workers to check if a file is being accessed and if it is, to wait until it's not before appending the output?
I thought something like Sys.sleep() before the write_csv command would work,as it would force each worker to wait a different amount of time before writing, but this doesn't appear to work in the testing I've done.